[mlir] Fix -Wsign-compare in MeshOps.cpp (NFC)

llvm-project/mlir/lib/Dialect/Mesh/IR/MeshOps.cpp:204:25:
 error: comparison of integers of different signs: 'size_t' (aka 'unsigned long') and 'int64_t' (aka 'long') [-Werror,-Wsign-compare]
  if (getShape().size() > rank)
      ~~~~~~~~~~~~~~~~~ ^ ~~~~
1 error generated.

Author: DamonFool

mlir/lib/Dialect/Mesh/IR/MeshOps.cpp

@@ -201,7 +201,7 @@ LogicalResult ClusterOp::verify() {
   if (rank <= 0)
     return emitOpError("rank of cluster is expected to be a positive integer");
 
-  if (getShape().size() > rank)
+  if (getShape().size() > size_t(rank))
     return emitOpError(
         "rank of shape is not expected to be larger than rank of cluster");