can: kvaser_usb: Use struct_size() in alloc_candev()

One of the more common cases of allocation size calculations is finding
the size of a structure that has a zero-sized array at the end, along
with memory for some number of elements for that array. For example:

struct foo {
    int stuff;
    void *entry[];
};

instance = alloc(sizeof(struct foo) + count * sizeof(void *));

Instead of leaving these open-coded and prone to type mistakes, we can
now use the new struct_size() helper:

instance = alloc(struct_size(instance, entry, count));

This code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

drivers/net/can/usb/kvaser_usb/kvaser_usb_core.c

@@ -643,8 +643,7 @@ static int kvaser_usb_init_one(struct kvaser_usb *dev,
 			return err;
 	}
 
-	netdev = alloc_candev(sizeof(*priv) +
-			      dev->max_tx_urbs * sizeof(*priv->tx_contexts),
+	netdev = alloc_candev(struct_size(priv, tx_contexts, dev->max_tx_urbs),
 			      dev->max_tx_urbs);
 	if (!netdev) {
 		dev_err(&dev->intf->dev, "Cannot alloc candev\n");