Merge pull request #7278 from pkuyym/fix-7216

Bug fix when inserting fill_zeros_like_op.

python/paddle/v2/fluid/backward.py

@@ -162,7 +162,7 @@ def _remove_no_grad_branch_(op_descs, no_grad_set):
             if core.grad_var_suffix() in arg and arg in no_grad_set:
                 to_insert.append((_create_op_desc_("fill_zeros_like", {
                     "X": [_strip_grad_suffix_(arg)]
-                }, {"Y": [arg]}, {}), idx))
+                }, {"Out": [arg]}, {}), idx))
 
     map(lambda p: op_descs.insert(p[1], p[0]), reversed(to_insert))