btrfs: update comment for temp-fsid, fsid, and metadata_uuid

Update the comment to explain the relationship between temp_fsid, fsid,
and metadata_uuid.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
1 file changed