Bug#541884: must use blkid instead of vol_id

[Christian Kujau]

Hi,

mdadm is still not available in unstable. I changed the rules file
as suggessted by Marco, dpkg-buildpackage'd it and was able to
install and use mdadm again[0]. If only a developer could do the
same and upload it... :-)

Thanks,
Christian.

[0] http://nerdbynature.de/bits/BTS-541884/