[LanRef] Fix typo in getelementptr example.

[bader]

Summary

Change B type from double to pointer to double.

[sanjoy]

lgtm

docs/LangRef.rst

getelementptr  %struct.ST, <4 x %struct.ST*> %s, <4 x i64> %ind1,
        i32 2, i32 1, <4 x i32> %ind4, i64 13
 
 Let's look at the C code, where the vector version of ``getelementptr``
 makes sense:
 
 .. code-block:: c
 
     // Let's assume that we vectorize the following loop:
-    double *A, B; int *C;
+    double *A, *B; int *C;
     for (int i = 0; i < size; ++i) {
       A[i] = B[C[i]];
     }
 
 .. code-block:: llvm
 
     ; get pointers for 8 elements from array B
     %ptrs = getelementptr double, double* %B, <8 x i32> %C