It causes
 # blockdev --report" error:
 blockdev: /dev/dm-9: failed to read partition start from sysfs: No such file or directory

There is no reliable way to detect a geometry in this case. Report N/A
instead.

Signed-off-by: Stanislav Brabec <sbrabec@suse.cz>
Cc: Martin Wilck <martin.wilck@suse.com>
Signed-off-by: Karel Zak <kzak@redhat.com>