fix xception precision problem (#22188)

Author: FrostML

paddle/fluid/framework/ir/graph_pattern_detector.cc

@@ -1441,6 +1441,7 @@ PDNode *patterns::ConvElementwiseadd::operator()(PDNode *conv_in) {
   auto elementwise_add_op = pattern->NewNode(elementwise_add_op_repr())
                                 ->assert_is_op("elementwise_add");
   auto elementwise_add_in_y = pattern->NewNode(elementwise_add_in_y_repr())
+                                  ->assert_is_persistable_var()
                                   ->assert_is_op_input("elementwise_add", "Y")
                                   ->AsInput();
   auto elementwise_add_out = pattern->NewNode(elementwise_add_out_repr())