ublk: remove two unused fields from 'struct ublk_queue'

Remove two unused fields(`io_addr` & `max_io_sz`) from `struct ublk_queue`.

Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250327095123.179113-4-ming.lei@redhat.com


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