io_uring: remove return from io_req_cqe_overflow()

Nobody checks io_req_cqe_overflow()'s return, make it return void.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8f2029ad0c22f73451664172d834372608ee0a77.1691757663.git.asml.silence@gmail.com


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