staging: vt6655: check ieee80211_bss_conf bssid not NULL

Sometimes bssid can go null on failed association.
Signed-off-by: NMalcolm Priestley <tvboxspy@gmail.com>
Cc: <stable@vger.kernel.org> # v3.19+
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vt6655/device_main.c

@@ -1418,7 +1418,7 @@ static void vnt_bss_info_changed(struct ieee80211_hw *hw,
 
 	priv->current_aid = conf->aid;
 
-	if (changed & BSS_CHANGED_BSSID) {
+	if (changed & BSS_CHANGED_BSSID && conf->bssid) {
 		unsigned long flags;
 
 		spin_lock_irqsave(&priv->lock, flags);