staging: wilc1000: fix return value check in wlan_initialize_threads()

In case of error, the function kthread_run() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Reviewed-by: Julian Calaby <julian.calaby@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wilc1000/linux_wlan.c

@@ -715,10 +715,10 @@ static int wlan_initialize_threads(struct net_device *dev)
 
 	wilc->txq_thread = kthread_run(linux_wlan_txq_task, (void *)dev,
 				     "K_TXQ_TASK");
-	if (!wilc->txq_thread) {
+	if (IS_ERR(wilc->txq_thread)) {
 		netdev_err(dev, "couldn't create TXQ thread\n");
 		wilc->close = 0;
-		return -ENOBUFS;
+		return PTR_ERR(wilc->txq_thread);
 	}
 	wait_for_completion(&wilc->txq_thread_started);