io_uring: consistently make use of io_notif_to_data()

This makes the assignment typesafe. It prepares
changing io_kiocb_to_cmd() in the next commit.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Link: https://lore.kernel.org/r/8da6e9d12cf95ad4bc73274406d12bca7aabf72e.1660201408.git.metze@samba.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>

io_uring/notif.c

@@ -100,7 +100,7 @@ __cold int io_notif_unregister(struct io_ring_ctx *ctx)
 
 		if (!notif)
 			continue;
-		nd = io_kiocb_to_cmd(notif);
+		nd = io_notif_to_data(notif);
 		slot->notif = NULL;
 		if (!refcount_dec_and_test(&nd->uarg.refcnt))
 			continue;