powerpc/pci: Check the bus address instead of resource address in pcibios_fixup_resources

If a BAR has the value of 0, we would assume that it is unset yet and
then mark the resource as unset and would reassign it later. But after
commit 6c5705fe

 (powerpc/PCI: get rid of device resource fixups)
the pcibios_fixup_resources is invoked after the bus address was
translated to linux resource. So the value of res->start is resource
address. And since the resource and bus address may be different, we
should translate it to the bus address before doing the check.

Signed-off-by: Kevin Hao <haokexin@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>