[pci] Correct invalid base-class/sub-class/prog-if order in PCIR

[pci] Correct invalid base-class/sub-class/prog-if order in PCIR

PCI Configuration Space contains fields prog-if at the offset 0x09,
sub-class at the offset 0x0a and base-class at the offset 0x0b (it
respects little endian).  PCIR structure uses these fields in the same
order.

Signed-off-by: Michael Brown <mcb30@ipxe.org>