btrfs: record btrfs_device directly in btrfs_io_bio

Instead of recording stripe_index and using that to access correct
btrfs_device from btrfs_bio::stripes record the btrfs_device in
btrfs_io_bio. This will enable endio handlers to increment device
error counters on checksum errors.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 75af233..5eea939 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -288,7 +288,7 @@ struct btrfs_fs_devices {
  */
 struct btrfs_io_bio {
 	unsigned int mirror_num;
-	unsigned int stripe_index;
+	struct btrfs_device *device;
 	u64 logical;
 	u8 *csum;
 	u8 csum_inline[BTRFS_BIO_INLINE_CSUM_SIZE];