Commit dccdb07b ("btrfs: kill btrfs_fs_info::volume_mutex") removed
the last use of the volume_mutex, forgetting to update the comment.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>