btrfs: Export btrfs_release_disk_super

Preparatory patch for removal of buffer_head usage in btrfs.
Signed-off-by: NNikolay Borisov <nborisov@suse.com>
Signed-off-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/volumes.c

@@ -1247,7 +1247,7 @@ int btrfs_open_devices(struct btrfs_fs_devices *fs_devices,
 	return ret;
 }
 
-static void btrfs_release_disk_super(struct page *page)
+void btrfs_release_disk_super(struct page *page)
 {
 	kunmap(page);
 	put_page(page);

fs/btrfs/volumes.h

@@ -484,6 +484,7 @@ int btrfs_finish_chunk_alloc(struct btrfs_trans_handle *trans,
 int btrfs_remove_chunk(struct btrfs_trans_handle *trans, u64 chunk_offset);
 struct extent_map *btrfs_get_chunk_map(struct btrfs_fs_info *fs_info,
 				       u64 logical, u64 length);
+void btrfs_release_disk_super(struct page *page);
 
 static inline void btrfs_dev_stat_inc(struct btrfs_device *dev,
 				      int index)