net: cw1200: fix a NULL pointer dereference

In case create_singlethread_workqueue fails, the fix free the
hardware and returns NULL to avoid NULL pointer dereference.
Signed-off-by: Kangjie Lu <kjlu@umn.edu>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/st/cw1200/main.c

@@ -345,6 +345,11 @@ static struct ieee80211_hw *cw1200_init_common(const u8 *macaddr,
 	mutex_init(&priv->wsm_cmd_mux);
 	mutex_init(&priv->conf_mutex);
 	priv->workqueue = create_singlethread_workqueue("cw1200_wq");
+	if (!priv->workqueue) {
+		ieee80211_free_hw(hw);
+		return NULL;
+	}
+
 	sema_init(&priv->scan.lock, 1);
 	INIT_WORK(&priv->scan.work, cw1200_scan_work);
 	INIT_DELAYED_WORK(&priv->scan.probe_work, cw1200_probe_work);