cxgb3/l2t: Use struct_size() in kvzalloc()

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;
    struct boo entry[];
};

size = sizeof(struct foo) + count * sizeof(struct boo);
instance = kvzalloc(size, GFP_KERNEL);

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

instance = kvzalloc(struct_size(instance, entry, count), GFP_KERNEL);

Notice that, in this case, variable size is not necessary, hence
it is removed.

This code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb3/l2t.c

@@ -443,9 +443,9 @@ void t3_l2t_update(struct t3cdev *dev, struct neighbour *neigh)
 struct l2t_data *t3_init_l2t(unsigned int l2t_capacity)
 {
 	struct l2t_data *d;
-	int i, size = sizeof(*d) + l2t_capacity * sizeof(struct l2t_entry);
+	int i;
 
-	d = kvzalloc(size, GFP_KERNEL);
+	d = kvzalloc(struct_size(d, l2tab, l2t_capacity), GFP_KERNEL);
 	if (!d)
 		return NULL;