pipe: add pipe_buf_steal() helper

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index e5d5cc9..17a706d 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -841,7 +841,7 @@
 	if (cs->len != PAGE_SIZE)
 		goto out_fallback;
 
-	if (buf->ops->steal(cs->pipe, buf) != 0)
+	if (pipe_buf_steal(cs->pipe, buf) != 0)
 		goto out_fallback;
 
 	newpage = buf->page;