ath9k: fix null pointer dereference in ani monitor code

In 'ath9k_ani_reset' the 'ahp->ah_curani' will be initialized only
if 'DO_ANI(ah)' true. In 'ath9k_hw_ani_monitor' we are using
'ahp->ah_curani' unconditionally, and it will cause a NULL pointer
dereference on AR9100.

Changes-licensed-under: ISC
Signed-off-by: NGabor Juhos <juhosg@openwrt.org>
Signed-off-by: NImre Kaloz <kaloz@openwrt.org>
Tested-by: NPavel Roskin <proski@gnu.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath9k/ani.c

@@ -551,6 +551,9 @@ void ath9k_hw_ani_monitor(struct ath_hal *ah,
 	struct ar5416AniState *aniState;
 	int32_t listenTime;
 
+	if (!DO_ANI(ah))
+		return;
+
 	aniState = ahp->ah_curani;
 	ahp->ah_stats.ast_nodestats = *stats;
 
@@ -610,9 +613,6 @@ void ath9k_hw_ani_monitor(struct ath_hal *ah,
 		aniState->cckPhyErrCount = cckPhyErrCnt;
 	}
 
-	if (!DO_ANI(ah))
-		return;
-
 	if (aniState->listenTime > 5 * ahp->ah_aniPeriod) {
 		if (aniState->ofdmPhyErrCount <= aniState->listenTime *
 		    aniState->ofdmTrigLow / 1000 &&