backlight: atmel-pwm-bl: fix gpio polarity in remove

Make sure to honour gpio polarity also at remove so that the backlight is
actually disabled on boards with active-low enable pin.

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