ACPI: video: fix acpi_backlight=video

Make "acpi_backlight=video" param enable ACPI_VIDEO_BACKLIGHT_FORCE_VIDEO
as intended, instead of incorrectly enabling video output switching.

BugLink: http://bugs.launchpad.net/bugs/573120
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Cc: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: <stable@kernel.org>
Acked-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>