ublk: pass ublksrv_ctrl_cmd * instead of io_uring_cmd *

ublk: pass ublksrv_ctrl_cmd * instead of io_uring_cmd *

The ublk_ctrl_*() handlers all take struct io_uring_cmd *cmd but only
use it to get struct ublksrv_ctrl_cmd *header from the io_uring SQE.
Since the caller ublk_ctrl_uring_cmd() has already computed header, pass
it instead of cmd.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://lore.kernel.org/r/20250409012928.3527198-1-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>