PCI: export __pci_remove_bus_device

Don't switch to pci_remove_bus_device yet, keep the __ prefix for now
(the behavior is still the same: remove without stopping first).

This allows other out of tree users or pending patches to get notified
from compiler warning.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>