block: use bd_partno in bdevname

No need to go through the hd_struct to find the partition number.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/genhd.c

@@ -85,7 +85,7 @@ char *disk_name(struct gendisk *hd, int partno, char *buf)
 
 const char *bdevname(struct block_device *bdev, char *buf)
 {
-	return disk_name(bdev->bd_disk, bdev->bd_part->partno, buf);
+	return disk_name(bdev->bd_disk, bdev->bd_partno, buf);
 }
 EXPORT_SYMBOL(bdevname);