ath9k: fix a crash that happens when survey stats are accessed before the interface is brought up for the first time

SVN-Revision: 23549

package/mac80211/patches/540-ath9k_fix_survey_crash.patch

@@ -0,0 +1,12 @@
+--- a/drivers/net/wireless/ath/ath9k/main.c
++++ b/drivers/net/wireless/ath/ath9k/main.c
+@@ -183,6 +183,9 @@ static void ath_update_survey_stats(stru
+ 	struct ath_cycle_counters *cc = &common->cc_survey;
+ 	unsigned int div = common->clockrate * 1000;
+ 
++	if (!ah->curchan)
++		return;
++
+ 	if (ah->power_mode == ATH9K_PM_AWAKE)
+ 		ath_hw_cycle_counters_update(common);
+