PCI: Assign CardBus bus number only during the second pass

Right now the CardBus code in pci_scan_bridge() is executed during both
passes. Since we always allocate the bus number ourselves it makes sense
to put it into the second pass.

Signed-off-by: Andreas Noever <andreas.noever@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>