The only caller doesn't handle the return value of io_put_kbuf_comp(), so
change its return type into void.

Also follow Jens's suggestion to rename it as io_put_kbuf_drop().
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20240407132759.4056167-1-ming.lei@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>