mt7601u: check memory allocation failure

Check memory allocation failure and return -ENOMEM in such a case, as
already done a few lines below.

As 'dev->tx_q' can be NULL, we also need to check for that in
'mt7601u_free_tx()', and return early.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Jakub Kicinski <kubakici@wp.pl>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/mediatek/mt7601u/dma.c

@@ -457,6 +457,9 @@ static void mt7601u_free_tx(struct mt7601u_dev *dev)
 {
 	int i;
 
+	if (!dev->tx_q)
+		return;
+
 	for (i = 0; i < __MT_EP_OUT_MAX; i++)
 		mt7601u_free_tx_queue(&dev->tx_q[i]);
 }
@@ -484,6 +487,8 @@ static int mt7601u_alloc_tx(struct mt7601u_dev *dev)
 
 	dev->tx_q = devm_kcalloc(dev->dev, __MT_EP_OUT_MAX,
 				 sizeof(*dev->tx_q), GFP_KERNEL);
+	if (!dev->tx_q)
+		return -ENOMEM;
 
 	for (i = 0; i < __MT_EP_OUT_MAX; i++)
 		if (mt7601u_alloc_tx_queue(dev, &dev->tx_q[i]))