UBUNTU: SAUCE: net/wireless: do not dereference invalid pointer

BugLink: https://launchpad.net/bugs/1712746

The wiphy may be NULL sometimes. Do not dereference when it's NULL.
Signed-off-by: Wen-chien Jesse Sung <jesse.sung@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-By: AceLan Kao <acelan.kao@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

net/wireless/util.c

@@ -121,7 +121,7 @@ struct ieee80211_channel *__ieee80211_get_channel(struct wiphy *wiphy,
 	int i;
 
 	for (band = 0; band < IEEE80211_NUM_BANDS; band++) {
-		sband = wiphy->bands[band];
+		sband = wiphy ? wiphy->bands[band] : NULL;
 
 		if (!sband)
 			continue;