ath9k: use the passed ieee80211_hw on ath_rx_prepare()

this now uses the proper hw which should mean finding the
right sta when using ath9k virtual wiphy stuff. Only
advantage I see here is getting the rssi properly updated
so the 'fix' itself isn't that great, but at least this
is correct.

Cc: Jouni.Malinen <Jouni.Malinen@atheros.com>
Signed-off-by: NLuis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -201,7 +201,7 @@ static int ath_rx_prepare(struct ieee80211_hw *hw,
 
 	rcu_read_lock();
 	/* XXX: use ieee80211_find_sta! */
-	sta = ieee80211_find_sta_by_hw(sc->hw, hdr->addr2);
+	sta = ieee80211_find_sta_by_hw(hw, hdr->addr2);
 	if (sta) {
 		an = (struct ath_node *) sta->drv_priv;
 		if (ds->ds_rxstat.rs_rssi != ATH9K_RSSI_BAD &&