Fix another buggy fake acpi pci root driver

Fix another buggy fake acpi pci root driver

In this case, the platform driver that creates the PCI(e) root device
doesn't fill in its driver link, so we can't look up what driver is in
use - but since it's the root, it *really* doesn't matter.  And in
general, we only really care if it's the last node in our path, because
that'll be the controller for the boot device anyway.

Signed-off-by: Peter Jones <pjones@redhat.com>