Make acpi_bus_get_parent() more straightforward and remove an
unnecessary local variable ret from it.
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Acked-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com> Acked-by: Yinghai Lu <yinghai@kernel.org> Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>