ublk: call io_uring_cmd_to_pdu to get uring_cmd pdu

Call io_uring_cmd_to_pdu() to get uring_cmd pdu, and one big benefit
is the automatic pdu size build check.

Suggested-by: Uday Shankar <ushankar@purestorage.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://lore.kernel.org/r/20250327095123.179113-6-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -1040,7 +1040,7 @@ static blk_status_t ublk_setup_iod(struct ublk_queue *ubq, struct request *req)
 static inline struct ublk_uring_cmd_pdu *ublk_get_uring_cmd_pdu(
 		struct io_uring_cmd *ioucmd)
 {
-	return (struct ublk_uring_cmd_pdu *)&ioucmd->pdu;
+	return io_uring_cmd_to_pdu(ioucmd, struct ublk_uring_cmd_pdu);
 }
 
 static inline bool ubq_daemon_is_dying(struct ublk_queue *ubq)