fix table grad send sync_mode

Author: jacquesqiao

python/paddle/fluid/transpiler/distribute_transpiler.py

@@ -1082,7 +1082,7 @@ def _split_table_grad_and_add_send_vars(self, program, pserver_endpoints):
                         if self.sync_mode else []
                     },
                     attrs={
-                        "sync_mode": False,
+                        "sync_mode": self.sync_mode,
                         "epmap": pserver_endpoints,
                         RPC_OP_ROLE_ATTR_NAME: RPC_OP_ROLE_ATTR_VALUE,
                         OP_ROLE_VAR_ATTR_NAME: [