drivers/video/backlight/tdo24m.c: add missing const

Add 'const' to static array that was missing it in its definition.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Eric Miao <eric.y.miao@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>