ACPI: video: fix brightness allocation

upstream commit 469778c1

Thanks to Arjan for spotting this
http://www.kerneloops.org/search.php?search=acpi_video_switch_brightness


and suggesting it for .stable


Fix use of uninitialized device->brightness.

Signed-off-by: Julia Jomantaite <julia.jomantaite@gmail.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>