ublk: skip 1 NULL check in ublk_cmd_list_tw_cb() loop

ublk_cmd_list_tw_cb() is always performed on a non-empty request list.
So don't check whether rq is NULL on the first iteration of the loop,
just on subsequent iterations.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Link: https://lore.kernel.org/r/20250328180411.2696494-3-csander@purestorage.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/ublk_drv.c

@@ -1290,12 +1290,12 @@ static void ublk_cmd_list_tw_cb(struct io_uring_cmd *cmd,
 	struct ublk_queue *ubq = rq->mq_hctx->driver_data;
 	struct request *next;
 
-	while (rq) {
+	do {
 		next = rq->rq_next;
 		rq->rq_next = NULL;
 		ublk_dispatch_req(ubq, rq, issue_flags);
 		rq = next;
-	}
+	} while (rq);
 }
 
 static void ublk_queue_cmd_list(struct ublk_queue *ubq, struct rq_list *l)