fix batch norm. test=develop (#15597)

paddle/fluid/operators/batch_norm_op.cc

@@ -589,8 +589,10 @@ class BatchNormGradMaker : public framework::SingleGradOpDescMaker {
     op->SetInput("SavedVariance", Output("SavedVariance"));
 
     // used when setting use_global_stats True during training
+    if (boost::get<bool>(GetAttr("use_global_stats"))) {
       op->SetInput("Mean", Output("MeanOut"));
       op->SetInput("Variance", Output("VarianceOut"));
+    }
 
     op->SetAttrMap(Attrs());