ublk: remove unnecessary ubq checks

ublk_init_queues() ensures that all nr_hw_queues queues are initialized,
with each ublk_queue's q_id set to its index. And ublk_init_queues() is
called before ublk_add_chdev(), which creates the cdev. Is is therefore
impossible for the !ubq || ub_cmd->q_id != ubq->q_id condition to hit in
__ublk_ch_uring_cmd(). Remove it to avoids some branches in the I/O path.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Uday Shankar <ushankar@purestorage.com>
Link: https://lore.kernel.org/r/20250416170154.3621609-1-csander@purestorage.com


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