[mlir] Fix warnings

This patch fixes:

  mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp:331:8:
  error: unused variable 'srcVecTy' [-Werror,-Wunused-variable]

  mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp:332:8:
  error: unused variable 'destVecTy' [-Werror,-Wunused-variable]

Author: kazutakahirata

mlir/lib/Dialect/Vector/Transforms/VectorEmulateNarrowType.cpp

@@ -332,6 +332,8 @@ static Value dynamicallyInsertSubVector(RewriterBase &rewriter, Location loc,
   auto destVecTy = cast<VectorType>(dest.getType());
   assert(srcVecTy.getRank() == 1 && destVecTy.getRank() == 1 &&
          "expected source and dest to be rank-1 vector types");
+  (void)srcVecTy;
+  (void)destVecTy;
   assert(numElemsToInsert > 0 &&
          "the number of elements to insert must be greater than 0");
   // NOTE: We are unable to take the offset into account in the following