pci/of: Consolidate pci_bus_to_OF_node()

The generic code always get the device-node in the right place now
so a single implementation will work for all archs

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Michal Simek <monstr@monstr.eu>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>