block: store a block_device pointer in struct bio

Replace the gendisk pointer in struct bio with a pointer to the newly
improved struct block device.  From that the gendisk can be trivially
accessed with an extra indirection, but it also allows to directly
look up all information related to partition remapping.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/drivers/block/rsxx/dev.c b/drivers/block/rsxx/dev.c
index edaceff..9a28322 100644
--- a/drivers/block/rsxx/dev.c
+++ b/drivers/block/rsxx/dev.c
@@ -122,7 +122,7 @@ static void bio_dma_done_cb(struct rsxx_cardinfo *card,
 
 static blk_qc_t rsxx_submit_bio(struct bio *bio)
 {
-	struct rsxx_cardinfo *card = bio->bi_disk->private_data;
+	struct rsxx_cardinfo *card = bio->bi_bdev->bd_disk->private_data;
 	struct rsxx_bio_meta *bio_meta;
 	blk_status_t st = BLK_STS_IOERR;