Modify comments of `sync_with_cpp`

python/paddle/fluid/framework.py

@@ -838,7 +838,7 @@ class Block(object):
 
     def sync_with_cpp(self):
         """
-        Sync with the desc on the c++ end.
+        Sync from the desc on the c++ end.
 
         This method is used to synchronize the c++ desc instance generated by backward.
         """