libblkid/minix: Match minix superblock types

libblkid/minix: Match minix superblock types

All of the types in the minix super block are unsigned but in
probe_minix they were being treated as signed. This would cause some of
the extra sanity checks to pass on a non minix device. The types were
updated to match the return types of the helper functions in
disk-utils/minix_programs.h

This can be checked by creating a swap partition with one of these UUIDs
35f1f264-2468-471a-bc85-acc9f4bc04a3
35f1f264-6824-471a-bc85-acc9f4bc04a3
35f1f264-2478-471a-bc85-acc9f4bc04a3
35f1f264-7824-471a-bc85-acc9f4bc04a3

Prior to this change they would all be considered minix and swap by
blkid.

Signed-off-by: Nate Clark <nate@neworld.us>