[MLIR] Fix tensor shapes in Toy chapter 1

[thopre]

Summary

In Toy tutorial chapter 1, multiply_transpose() is called with b<2, 3>
and c<3, 2> when both parameters should have the same shape. This commit
fixes this by instead using c and d as parameters and fix a comment typo
where c and d are mentioned to have shape <2, 2> when they actually have
shape <3, 2>.

mlir/docs/Tutorials/Toy/Ch-1.md

def main() {
   var c = multiply_transpose(a, b);
 
   # A second call to `multiply_transpose` with <2, 3> for both arguments will
   # reuse the previously specialized and inferred version and return <3, 2>.
   var d = multiply_transpose(b, a);
 
   # A new call with <3, 2> (instead of <2, 3>) for both dimensions will
   # trigger another specialization of `multiply_transpose`.
-  var e = multiply_transpose(b, c);
+  var e = multiply_transpose(c, d);
 
   # Finally, calling into `multiply_transpose` with incompatible shape will
   # trigger a shape inference error.
   var f = multiply_transpose(transpose(a), c);
 }
 ```
 
 ## The AST
Block {
         ]
       VarDecl d<> @test/Examples/Toy/Ch1/ast.toy:22:3
         Call 'multiply_transpose' [ @test/Examples/Toy/Ch1/ast.toy:22:11
           var: b @test/Examples/Toy/Ch1/ast.toy:22:30
           var: a @test/Examples/Toy/Ch1/ast.toy:22:33
         ]
       VarDecl e<> @test/Examples/Toy/Ch1/ast.toy:25:3
         Call 'multiply_transpose' [ @test/Examples/Toy/Ch1/ast.toy:25:11
-          var: b @test/Examples/Toy/Ch1/ast.toy:25:30
-          var: c @test/Examples/Toy/Ch1/ast.toy:25:33
+          var: c @test/Examples/Toy/Ch1/ast.toy:25:30
+          var: d @test/Examples/Toy/Ch1/ast.toy:25:33
         ]
       VarDecl f<> @test/Examples/Toy/Ch1/ast.toy:28:3
         Call 'multiply_transpose' [ @test/Examples/Toy/Ch1/ast.toy:28:11
           Call 'transpose' [ @test/Examples/Toy/Ch1/ast.toy:28:30
             var: a @test/Examples/Toy/Ch1/ast.toy:28:40
           ]
           var: c @test/Examples/Toy/Ch1/ast.toy:28:44
         ]

mlir/test/Examples/Toy/Ch1/ast.toy

def main() {
   # The shape is inferred from the supplied literal.
   var a = [[1, 2, 3], [4, 5, 6]];
   # b is identical to a, the literal array is implicitly reshaped: defining new
   # variables is the way to reshape arrays (element count in literal must match
   # the size of specified shape).
   var b<2, 3> = [1, 2, 3, 4, 5, 6];
 
   # This call will specialize `multiply_transpose` with <2, 3> for both
-  # arguments and deduce a return type of <2, 2> in initialization of `c`.
+  # arguments and deduce a return type of <3, 2> in initialization of `c`.
   var c = multiply_transpose(a, b);
   # A second call to `multiply_transpose` with <2, 3> for both arguments will
-  # reuse the previously specialized and inferred version and return `<2, 2>`
+  # reuse the previously specialized and inferred version and return `<3, 2>`
   var d = multiply_transpose(b, a);
-  # A new call with `<2, 2>` for both dimension will trigger another
+  # A new call with `<3, 2>` for both dimension will trigger another
   # specialization of `multiply_transpose`.
-  var e = multiply_transpose(b, c);
+  var e = multiply_transpose(c, d);
   # Finally, calling into `multiply_transpose` with incompatible shape will
   # trigger a shape inference error.
   var f = multiply_transpose(transpose(a), c);
 }
 
 
 # CHECK: Module:
 # CHECK-NEXT:     Function

 # CHECK-NEXT:           ]
 # CHECK-NEXT:         VarDecl d<> @{{.*}}ast.toy:22:3
 # CHECK-NEXT:           Call 'multiply_transpose' [ @{{.*}}ast.toy:22:11
 # CHECK-NEXT:             var: b @{{.*}}ast.toy:22:30
 # CHECK-NEXT:             var: a @{{.*}}ast.toy:22:33
 # CHECK-NEXT:           ]
 # CHECK-NEXT:         VarDecl e<> @{{.*}}ast.toy:25:3
 # CHECK-NEXT:           Call 'multiply_transpose' [ @{{.*}}ast.toy:25:11
-# CHECK-NEXT:             var: b @{{.*}}ast.toy:25:30
-# CHECK-NEXT:             var: c @{{.*}}ast.toy:25:33
+# CHECK-NEXT:             var: c @{{.*}}ast.toy:25:30
+# CHECK-NEXT:             var: d @{{.*}}ast.toy:25:33
 # CHECK-NEXT:           ]
 # CHECK-NEXT:         VarDecl f<> @{{.*}}ast.toy:28:3
 # CHECK-NEXT:           Call 'multiply_transpose' [ @{{.*}}ast.toy:28:11
 # CHECK-NEXT:             Call 'transpose' [ @{{.*}}ast.toy:28:30
 # CHECK-NEXT:               var: a @{{.*}}ast.toy:28:40
 # CHECK-NEXT:             ]
 # CHECK-NEXT:             var: c @{{.*}}ast.toy:28:44
 # CHECK-NEXT:           ]