backlight: initialize struct backlight_properties properly

In all these files, the .power field was never correctly initialized.

Signed-off-by: Corentin Chary <corentin.chary@gmail.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Cc: Dave Airlie <airlied@gmail.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>