!13024 Fix bprop dynamic top cell

From: @zjun3021
Reviewed-by: @kisnwang,@chujinjin
Signed-off-by: @chujinjin

mindspore/ccsrc/pipeline/pynative/pynative_execute.cc

@@ -2537,7 +2537,7 @@ void PynativeExecutor::GradNetInner(const GradOperationPtr &grad, const py::obje
 }
 
 void PynativeExecutor::ClearDynamicTopRes(const std::string &cell_id, const FuncGraphPtr &df_builder) {
-  if (IsTopestGraph(cell_id)) {
+  if (df_builder == nullptr && IsTopestGraph(cell_id)) {
     op_index_map_.clear();
   }
   // Delete unused top cell resource