I think that if a PCI bus is a root bus, attached to a host bridge not a

PCI->PCI bridge, then bus->self is allowed to be NULL. Certainly that's
the case on my Pegasos, and it makes the MGA DRM driver oops...

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>