qtnfmac: fix NULL pointer dereference

In case *vif* is NULL at 655: if (!vif), the execution path jumps to
label out, where *vif* is dereferenced at 679:

if (vif->sta_state == QTNF_STA_CONNECTING)

Fix this by immediately returning when *vif* is NULL instead of
jumping to label out.

Addresses-Coverity-ID: 1469567 ("Dereference after null check")
Fixes: 480daa9cb62c ("qtnfmac: fix invalid STA state on EAPOL failure")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Sergey Matyukevich <sergey.matyukevich.os@quanenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

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

@@ -654,8 +654,7 @@ qtnf_disconnect(struct wiphy *wiphy, struct net_device *dev,
 	vif = qtnf_mac_get_base_vif(mac);
 	if (!vif) {
 		pr_err("MAC%u: primary VIF is not configured\n", mac->macid);
-		ret = -EFAULT;
-		goto out;
+		return -EFAULT;
 	}
 
 	if (vif->wdev.iftype != NL80211_IFTYPE_STATION) {