rtlwifi: fix a potential NULL pointer dereference

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

drivers/net/wireless/realtek/rtlwifi/base.c

@@ -448,6 +448,11 @@ static void _rtl_init_deferred_work(struct ieee80211_hw *hw)
 	/* <2> work queue */
 	rtlpriv->works.hw = hw;
 	rtlpriv->works.rtl_wq = alloc_workqueue("%s", 0, 0, rtlpriv->cfg->name);
+	if (unlikely(!rtlpriv->works.rtl_wq)) {
+		pr_err("Failed to allocate work queue\n");
+		return;
+	}
+
 	INIT_DELAYED_WORK(&rtlpriv->works.watchdog_wq,
 			  (void *)rtl_watchdog_wq_callback);
 	INIT_DELAYED_WORK(&rtlpriv->works.ips_nic_off_wq,