ACPI video: fix an error when the brightness levels on AC and on Battery are same

when the brightness level on AC and brightness level on Battery
are same, the level_ac_battery is 1 in the current code,
which is wrong.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
1 file changed