fix op name typo

Author: Yancey0623

paddle/fluid/framework/details/multi_devices_graph_builder.cc

@@ -230,10 +230,10 @@ std::unique_ptr<SSAGraph> MultiDevSSAGraphBuilder::Build(
         }
         CreateDistTrainOp(&result, *op, rpc_op_device_id);
       }
-      if (op->Type() == "oncat") {
+      if (op->Type() == "concat") {
         auto got = remote_vars_devices_.find(op->InputArgumentNames()[0]);
-        PADDLE_ENFORCE_NE(got != remote_vars_devices_.end(),
-                          "can not find right place to concat received var.");
+        PADDLE_ENFORCE(got != remote_vars_devices_.end(),
+                       "can not find right place to concat received var.");
         CreateDistTrainOp(&result, *op, got->second);
       } else {
         CreateDistTrainOp(&result, *op, 0);