net: dsa: loop: Check for memory allocation failure

If 'devm_kzalloc' fails, a NULL pointer will be dereferenced.
Return -ENOMEM instead, as done for some other memory allocation just a
few lines above.

Fixes: 98cd1552ea27 ("net: dsa: Mock-up driver")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/dsa_loop.c

@@ -256,6 +256,9 @@ static int dsa_loop_drv_probe(struct mdio_device *mdiodev)
 		return -ENOMEM;
 
 	ps = devm_kzalloc(&mdiodev->dev, sizeof(*ps), GFP_KERNEL);
+	if (!ps)
+		return -ENOMEM;
+
 	ps->netdev = dev_get_by_name(&init_net, pdata->netdev);
 	if (!ps->netdev)
 		return -EPROBE_DEFER;