ar9170: fix LED power state handling

This patch fixes a minor visual bug in the led code, which
left the LED in the wrong power state when it was toggled
in a _unexpected_ way (e.g: enabling the LED twice).

Signed-off-by: Christian Lamparter <chunkeey@web.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>