drivers/video/backlight/ot200_bl.c: use devm_ functions

The devm_ functions allocate memory that is released when a driver
detaches. This patch uses devm_kzalloc of these functions

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Christian Gmeiner <christian.gmeiner@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>