ath9k: Fix function argument type

ath9k_vif_iter() was earlier used as an iterator
routine when calling a mac80211 utility. This is no
longer the case and hence we can mention the argument
type explicitly.
Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/ath9k/main.c

@@ -893,9 +893,9 @@ static bool ath9k_uses_beacons(int type)
 	}
 }
 
-static void ath9k_vif_iter(void *data, u8 *mac, struct ieee80211_vif *vif)
+static void ath9k_vif_iter(struct ath9k_vif_iter_data *iter_data,
+			   u8 *mac, struct ieee80211_vif *vif)
 {
-	struct ath9k_vif_iter_data *iter_data = data;
 	int i;
 
 	if (iter_data->has_hw_macaddr) {