drivers/video/backlight/atmel-pwm-bl.c: use module_platform_driver_probe()

Use the module_platform_driver_probe() macro which makes the code
smaller and simpler.

Signed-off-by: Jingoo Han <jg1.han@samsung.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>