powerpc/pci: Fix PCI<->OF matching of old style multifunc devices

Old OF variants used to create a 'dummy' parent node "multifunc-device"
for devices with more than one PCI function. Our code that matches OF
nodes to PCI devices dealt with that in one place but not in another,
this fixes it.

This has the practical effect of fixing interrupt routing of multifunction
PCI cards on some older PowerMac machines.

Signed-off-by: Tom Arbuckle <tom.d.arbuckle@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>