ub: Ignore bad residue

I hoped to continue to ignore this problem or use libusual, but these
days it's simpler to work around than to deal with it. Let's attempt to
use bad residue devices and hope that upper level integrity checks catch
any problems (e.g. please use sha1sum on your backups).

Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>