ublk: move fake timeout logic into __ublk_complete_rq()

Almost every block driver deals with fake timeout logic around real
request completion code.

Also the existing way may cause request reference count leak, so move the
logic into __ublk_complete_rq(), then we can skip the completion in the
last step like other drivers.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250713143415.2857561-4-ming.lei@redhat.com


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