libfdisk: gpt: loosen check fot pmbr size in lba

libfdisk: gpt: loosen check fot pmbr size in lba

While most disk partitioning tools out there create a pMBR's size in lba
to be the lesser of the whole disk or 2Tib, Microsoft apparently does not[1].
It always sets the entry to the maximum 32-bit limitation - even though a
drive may be smaller than that.

Loosen this check and only verify that the size is either the whole disk
or 0xFFFFFFFF.  No tool in its right mind would set it to any value
other than these.

[1] http://thestarman.pcministry.com/asm/mbr/GPT.htm#GPTPT

Signed-off-by: Davidlohr Bueso <davidlohr@hp.com>