ath9k: Fix kernel panic on module unload

The commit "ath9k: configure beacons based on hw opmode" introduced
a regression which leads to kernel panic. Failed to stop ani timer
during the driver unload while any of the beaconing vif is running.
Signed-off-by: NRajkumar Manoharan <rmanoharan@atheros.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

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

@@ -320,6 +320,7 @@ void ath_beacon_return(struct ath_softc *sc, struct ath_vif *avp)
 	if (avp->av_bcbuf != NULL) {
 		struct ath_buf *bf;
 
+		avp->is_bslot_active = false;
 		if (avp->av_bslot != -1) {
 			sc->beacon.bslot[avp->av_bslot] = NULL;
 			sc->nbcnvifs--;

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

@@ -1375,6 +1375,9 @@ static void ath9k_calculate_summary_state(struct ieee80211_hw *hw,
 	if ((iter_data.naps + iter_data.nadhocs) > 0) {
 		sc->sc_flags |= SC_OP_ANI_RUN;
 		ath_start_ani(common);
+	} else {
+		sc->sc_flags &= ~SC_OP_ANI_RUN;
+		del_timer_sync(&common->ani.timer);
 	}
 }