!4116 fix bug：add split opt pass on pynative mode

Merge pull request !4116 from jjfeing/master

mindspore/ccsrc/backend/optimizer/ascend/ascend_backend_optimization.cc

@@ -308,6 +308,7 @@ void RunOpAscendBackendIRFusionOptimization(const std::shared_ptr<session::Kerne
   }
   auto optimizer = std::make_shared<GraphOptimizer>();
   auto ir_fusion_pm = std::make_shared<PassManager>("ir_fusion_pm");
+  ir_fusion_pm->AddPass(std::make_shared<SplitFission>());
   ir_fusion_pm->AddPass(std::make_shared<BnSplit>());
   ir_fusion_pm->AddPass(std::make_shared<LayerNormGradSplit>());
   ir_fusion_pm->AddPass(std::make_shared<TopKSplit>());