[mlir] [docs] Broken link in MLIR Toy docs

[Wheest]

Summary

In the Ch6 of the Toy Example for MLIR, there is a broken link. If ones goes to the page for Chapter 6, and click on the link "Conversion to the LLVM IR Dialect", one will see it takes you to a page that no longer exists.

I believe this should actually be this link.

Note to reviewers that this is my first submitted patch to LLVM, and using the phabricator system, so there is a higher risk that I have made an error, and brief feedback on these patch notes would be appreciated.

Reviewer rational: Users who git blame say contributed to the tutorial.

I believe that automated tests on these markdown docs could reduce the risk of this kind of error occurring again. For example, this Python package checks for broken markdown links. However, I am unsure where in the existing testing infrastructure this could go, I am only somewhat familiar with the C++ side.

[Wheest]

Thanks, if the reviewers are happy, then I request that this gets pushed.

I don't think I have commit access, in which case, my preferred git author line would be Perry Gibson <[e-mail]>.

mlir/docs/Tutorials/Toy/Ch-6.md

^bb18:
   llvm.call @free(%238) : (!llvm<"i8*">) -> ()
   %239 = llvm.extractvalue %25[0] : !llvm<"{ double*, i64, [2 x i64], [2 x i64] }">
   %240 = llvm.bitcast %239 : !llvm<"double*"> to !llvm<"i8*">
   llvm.call @free(%240) : (!llvm<"i8*">) -> ()
   llvm.return
 }
 ```
 
-See [Conversion to the LLVM IR Dialect](../../ConversionToLLVMDialect.md) for
+See [LLVM IR Target](../../TargetLLVMIR.md) for
 more in-depth details on lowering to the LLVM dialect.
 
 ## CodeGen: Getting Out of MLIR
 
 At this point we are right at the cusp of code generation. We can generate code
 in the LLVM dialect, so now we just need to export to LLVM IR and setup a JIT to
 run it.