caif: fix NULL pointer check

Reported-by: <rucsoftsec@gmail.com>
Resolves-bug: http://bugzilla.kernel.org/show_bug?44441
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/caif/caif_serial.c

@@ -325,6 +325,9 @@ static int ldisc_open(struct tty_struct *tty)
 
 	sprintf(name, "cf%s", tty->name);
 	dev = alloc_netdev(sizeof(*ser), name, caifdev_setup);
+	if (!dev)
+		return -ENOMEM;
+
 	ser = netdev_priv(dev);
 	ser->tty = tty_kref_get(tty);
 	ser->dev = dev;