libblkid: (nilfs2) check devise size

libblkid: (nilfs2) check devise size

Unfortunately, nilfs2 have the same problem like many RAIDs. It uses
the end of the device to store (backup) superblock. The end of the
last partition is the same location as the end of the whole-disk. It
means that the superblock seems valid for the last partitions as well
as for whole-device.

Fortunately, nilfs2 superblock contains size of the device, so we can
distinguish between whole-disk and partition device.

Reported-by: Heinz Diehl <htd+ml@fritha.org>
Signed-off-by: Karel Zak <kzak@redhat.com>