Per PCIe base specification (Revision 3.1a), section 7.5.3, type 1
configuration space header should be used when accessing PCIe switch.  So
we need to reconfigure the header according to the bus number we are
accessing.  Otherwise we could not visit the buses behind the switch.
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>