Fix compile error

Author: JiayiFeng

paddle/operators/add_op_test.cc

@@ -22,7 +22,7 @@ TEST(AddOp, GetOpProto) {
  auto& protos = paddle::framework::OpRegistry::protos();
  auto it = protos.find("add_two");
  ASSERT_NE(it, protos.end());
- auto& grad_creators = paddle::framework::OpRegistry::grad_creators();
- auto it1 = grad_creators.find("add_two");
- ASSERT_NE(it1, grad_creators.end());
+ auto& op_creators = paddle::framework::OpRegistry::op_creators();
+ auto it1 = op_creators.find("add_two_grad");
+ ASSERT_NE(it1, op_creators.end());
 }