sony-laptop: do not scribble keyboard backlight registers on resume

Follow-up to commit 294d31e8

 ("sony-laptop: don't change keyboard
backlight settings"): avoid messing up the state on resume.  Leave it to
what was before suspending as it's anyway likely that we still don't
know what value we should write to the EC registers.  This fix is also
required in 3.12

Cc: stable@vger.kernel.org
Tested-by: Karol Babioch <karol@babioch.de>
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>