minor fix

Signed-off-by: YunLiu <55491388+KumoLiu@users.noreply.github.com>

monai/transforms/spatial/functional.py

@@ -258,6 +258,7 @@ def flip_helper(data, sp_size, sp_axes, lazy, transform_info):
     )
     return axes, meta_info
 
+
 def flip_image(img, sp_axes, lazy, transform_info):
     """
     Functional implementation of flip.