io_uring/net: fix must_hold annotation

Fix up the io_alloc_notif()'s __must_hold as we don't have a ctx
argument there but should get it from the slot instead.

Reported-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/cbb0a920f18e0aed590bf58300af817b9befb8a3.1661342812.git.asml.silence@gmail.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>