x86/uv/x2apic: update for change in pci bridge handling.

When I added 3448a19d
I forgot about the special uv handling code for this, so this
patch fixes it up.

Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Acked-by: Ingo Molnar
Signed-off-by: Dave Airlie <airlied@redhat.com>