Bail out if we don't find an enclosing IOC.  Previously, if we didn't
find one, we tried to set things up using garbage for the SBA/IOC register
address, which causes a crash.

This crash only happens if firmware supplies a defective ACPI namespace, so
it doesn't fix any problems in the field.
Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>