fujitsu-laptop: use FB_BLANK_* constants

Replace the magic numbers in fujitsu-laptop.c by the appropriate FB_BLANK
constants, as indicated by the comment for backlight_properties.power in
include/linux/backlight.h.

Signed-off-by: Michael Karcher <kernel@mkarcher.dialup.fu-berlin.de>
Acked-by: Jonathan Woithe <jwoithe@just42.net>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>