io_uring: make io_sqpoll_wait_sq return void

Change the return type to void since it always return 0, and no need
to do the checking in syscall io_uring_enter.

Signed-off-by: Quanfa Fu <quanfafu@gmail.com>
Link: https://lore.kernel.org/r/20230115071519.554282-1-quanfafu@gmail.com


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