ath9k: cleanup led_pin initial

Make ath_init_leds() and ath_deinit_leds() pairs as the only
API to set leds, also removed direction configuration from
ath9k_start() and ath9k_stop(). So the initial is more clear
now.

Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>