staging: vt6656: check ieee80211_bss_conf bssid not NULL

commit d309509f upstream.

Sometimes bssid can go null on failed association.
Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/staging/vt6656/main_usb.c

@@ -700,7 +700,7 @@ 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)
 		vnt_mac_set_bssid_addr(priv, (u8 *)conf->bssid);