null_blk: stop using ->queuedata for bio mode

Instead of setting up the queuedata as well just use one private data
field.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/null_blk_main.c

@@ -1392,7 +1392,7 @@ static blk_qc_t null_queue_bio(struct request_queue *q, struct bio *bio)
 {
 	sector_t sector = bio->bi_iter.bi_sector;
 	sector_t nr_sectors = bio_sectors(bio);
-	struct nullb *nullb = q->queuedata;
+	struct nullb *nullb = bio->bi_disk->private_data;
 	struct nullb_queue *nq = nullb_to_queue(nullb);
 	struct nullb_cmd *cmd;