ath9k: prepare for multi-interface CSA support

Soon mac80211 will support multi-interface CSA so
using sc->csa_vif is not an option.

Instead just depend on vif->csa_active. Calling
ieee80211_csa_finish() multiple number of times
should not be an issue.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/ath/ath9k/main.c b/drivers/net/wireless/ath/ath9k/main.c
index 5924f72d..317fcb9 100644
--- a/drivers/net/wireless/ath/ath9k/main.c
+++ b/drivers/net/wireless/ath/ath9k/main.c
@@ -1178,9 +1178,6 @@
 	if (ath9k_uses_beacons(vif->type))
 		ath9k_beacon_remove_slot(sc, vif);
 
-	if (sc->csa_vif == vif)
-		sc->csa_vif = NULL;
-
 	ath9k_ps_wakeup(sc);
 	ath9k_calculate_summary_state(hw, NULL);
 	ath9k_ps_restore(sc);
@@ -2086,13 +2083,8 @@
 					struct ieee80211_vif *vif,
 					struct cfg80211_chan_def *chandef)
 {
-	struct ath_softc *sc = hw->priv;
-
-	/* mac80211 does not support CSA in multi-if cases (yet) */
-	if (WARN_ON(sc->csa_vif))
-		return;
-
-	sc->csa_vif = vif;
+	/* depend on vif->csa_active only */
+	return;
 }
 
 struct ieee80211_ops ath9k_ops = {