PCI: Bus number from the bridge, not the device

PCI: Bus number from the bridge, not the device

pcibus_dev_print() was erroneously retrieving the device bus
number from the secondary bus number offset of the device
instead of the bridge above the device.  This ends of landing
in the 2nd byte of the 3rd BAR for devices, which thankfully
is usually zero.

Note: pcibus_get_dev_path() copied this code,
inheriting the same bug.  pcibus_get_dev_path() is used for
ramblock naming, so changing it can effect migration.  However,
I've only seen this byte be non-zero for an assigned device,
which can't migrate anyway, so hopefully we won't run into
any issues.

This patch does not touch pcibus_get_dev_path, as
bus number is guest assigned for nested buses,
so using it for migration is broken anyway.
Fix it properly later.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>