backlight: atmel-pwm-bl: use gpio_request_one

Use devm_gpio_request_one rather than requesting and setting direction
in two calls.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Cc: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>