qtnfmac: remove set but not used variable 'vif'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/net/wireless/quantenna/qtnfmac/cfg80211.c: In function 'qtnf_dump_survey':
drivers/net/wireless/quantenna/qtnfmac/cfg80211.c:694:19: warning:
 variable 'vif' set but not used [-Wunused-but-set-variable]
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/quantenna/qtnfmac/cfg80211.c

@@ -691,11 +691,8 @@ qtnf_dump_survey(struct wiphy *wiphy, struct net_device *dev,
 	const struct cfg80211_chan_def *chandef = &wdev->chandef;
 	struct ieee80211_channel *chan;
 	struct qtnf_chan_stats stats;
-	struct qtnf_vif *vif;
 	int ret;
 
-	vif = qtnf_netdev_get_priv(dev);
-
 	sband = wiphy->bands[NL80211_BAND_2GHZ];
 	if (sband && idx >= sband->n_channels) {
 		idx -= sband->n_channels;