samsung-laptop: don't handle backlight if handled by acpi/video

samsung-laptop: don't handle backlight if handled by acpi/video

commit f34cd9ca9320876e9c12764f052004628a03ba2d upstream.

samsung-laptop is not at all related to ACPI, but since this interface
is not documented at all, and the driver has to use it at load to
understand how it works on the laptop, I think it's a good idea to
disable it if a better solution is available.

Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Matthew Garrett <mjg@redhat.com>
[bwh: Backported to 3.2:
 - Adjust context, and change return to goto, since we do not have commit
   5dea7a2 ('samsung-laptop: move code into init/exit functions')
 - Use static variable since we do not have commit a6df489
   ('samsung-laptop: put all local variables in a single structure')]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>