libblkid: fix swap-area version

 * v1: hdr->version = 1, magic string = SWAPSPACE2
 * v0: no versio in header, magic string = SWAP-SPACE

The mistake has been introduced in the old udev volume_id
binary where the version was set according to magic string.

Reported-by: Phillip Susi <psusi@ubuntu.com>
Signed-off-by: Karel Zak <kzak@redhat.com>