ublk: add helper of ublk_need_map_io()

ublk_need_map_io() is more readable.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-5-ming.lei@redhat.com


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