mac80211: fix function pointer check

This makes "iw wlan0 dump survey" work again with
mac80211-based drivers that support it, e.g. ath5k.
Signed-off-by: NHolger Schurig <holgerschurig@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

net/mac80211/driver-ops.h

@@ -349,7 +349,7 @@ static inline int drv_get_survey(struct ieee80211_local *local, int idx,
 				struct survey_info *survey)
 {
 	int ret = -EOPNOTSUPP;
-	if (local->ops->conf_tx)
+	if (local->ops->get_survey)
 		ret = local->ops->get_survey(&local->hw, idx, survey);
 	/* trace_drv_get_survey(local, idx, survey, ret); */
 	return ret;