ar9170: fix build error when !CONFIG_AR9170_LEDS

Fix this build error when CONFIG_AR9170_LEDS is not set
drivers/net/wireless/ath/ar9170/main.c:1296: error: 'struct ar9170' has
no member named 'led_work'

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ar9170/main.c

@@ -1293,7 +1293,9 @@ static void ar9170_op_stop(struct ieee80211_hw *hw)
 	flush_workqueue(ar->hw->workqueue);
 
 	cancel_delayed_work_sync(&ar->tx_janitor);
+#ifdef CONFIG_AR9170_LEDS
 	cancel_delayed_work_sync(&ar->led_work);
+#endif
 	cancel_work_sync(&ar->filter_config_work);
 	cancel_work_sync(&ar->beacon_work);
 	mutex_lock(&ar->mutex);