[mlir] Fix a warning

This patch fixes:

  llvm-project/mlir/lib/Dialect/Linalg/IR/LinalgOps.cpp:1855:17:
  error: comparison of integers of different signs: 'int64_t' (aka
  'long') and 'size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]

Author: kazutakahirata

mlir/lib/Dialect/Linalg/IR/LinalgOps.cpp

@@ -1852,7 +1852,7 @@ LogicalResult BroadcastOp::verify() {
   auto inputShape = inputType.getShape();
   auto initShape = initType.getShape();
 
-  if (inputRank != dimensionsRef.size())
+  if ((size_t)inputRank != dimensionsRef.size())
     return emitOpError()
            << "input rank does match the number of dimensions. expected: "
            << inputRank << ", got: " << dimensionsRef.size();