[MLIR] Minor improvement to elementwise LIT test (#3666)

test/mlir/ngraph_dialect/elementwise_binary_ops.mlir

 // RUN: ngraph-opt %s | FileCheck %s
+// Verify the printed output can be parsed.
+// RUN: ngraph-opt %s | ngraph-opt | FileCheck %s
 
 // These tests verify the parser, builder and printer of element-wise binary ops.
 
 // CHECK-LABEL: func @add_float
 func @add_float(%arg0: !ng.tensor<2x2xf32>, %arg1: !ng.tensor<2x2xf32>) -> !ng.tensor<2x2xf32> {
-  // CHECK: ng.add
+  // CHECK: %{{[0-9]+}} = "ng.add"(%{{.*}}, %{{.*}}) : (!ng.tensor<2x2xf32>, !ng.tensor<2x2xf32>) -> !ng.tensor<2x2xf32>
   %0 = "ng.add"(%arg1, %arg0) : (!ng.tensor<2x2xf32>, !ng.tensor<2x2xf32>) -> !ng.tensor<2x2xf32>
   "ng.return"(%0) : (!ng.tensor<2x2xf32>) -> ()
 }