drivers/video/backlight/atmel-pwm-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>
Acked-by: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>