btrfs: store a block_device in struct btrfs_ordered_extent

Store the block device instead of the gendisk in the btrfs_ordered_extent
structure instead of acquiring a reference to it later.

Note: this is from series removing bdgrab/bdput, btrfs is one of the
last users.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8f60314..0117d86 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2992,7 +2992,7 @@ static int btrfs_finish_ordered_io(struct btrfs_ordered_extent *ordered_extent)
 		goto out;
 	}
 
-	if (ordered_extent->disk)
+	if (ordered_extent->bdev)
 		btrfs_rewrite_logical_zoned(ordered_extent);
 
 	btrfs_free_io_failure_record(inode, start, end);