[POWERPC] Remove bogus sanity check in pci -> OF node code

The new implementation of pci_device_to_OF_node() on ppc32 has a bogus
sanity check in it that can cause oopses at boot when no device node is
present, and might hit correct cases with older/weird apple device-trees
where they have the type "vci" for the chaos bridge.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>