btrfs: document fs_info in btrfs_rmap_block

Fixes fs/btrfs/block-group.c:1570: warning: Function parameter or member 'fs_info' not described in 'btrfs_rmap_block'
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/block-group.c

@@ -1561,7 +1561,9 @@ static void set_avail_alloc_bits(struct btrfs_fs_info *fs_info, u64 flags)
 }
 
 /**
- * btrfs_rmap_block - Map a physical disk address to a list of logical addresses
+ * Map a physical disk address to a list of logical addresses
+ *
+ * @fs_info:       the filesystem
  * @chunk_start:   logical address of block group
  * @physical:	   physical address to map to logical addresses
  * @logical:	   return array of logical addresses which map to @physical