Fix bus error when accessing MBR partition records

Fix bus error when accessing MBR partition records

Since the MBR layout only has partition records as 2-byte aligned, the
32-bit fields in them are not aligned. Thus, they cannot be accessed on
some architectures (such as SPARC) by using a "struct MBR_part_record *"
pointer, as the compiler can assume that the pointer is properly aligned.
Instead, the records must be accessed by going through the MBR struct
itself every time.

Signed-off-by: James Clarke <jrtc27@jrtc27.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>