driver core: try parent numa_node at first before using default

in the device_add, we try to use use parent numa_node.
need to make sure pci root bus's bridge device numa_node is set.
then we could use device->numa_node direclty for all device.
and don't need to call pcibus_to_node().

Signed-off-by: Yinghai Lu <yinghai.lu@sun.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>