For SQPOLL io_uring we want to have only one file note held by
sqo_task. Add a warning to make sure it holds. It's deep in
io_uring_add_task_file() out of hot path, so shouldn't hurt.
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>