cxgb4: smt: 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[];
};

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

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

drivers/net/ethernet/chelsio/cxgb4/smt.c

@@ -47,8 +47,7 @@ struct smt_data *t4_init_smt(void)
 
 	smt_size = SMT_SIZE;
 
-	s = kvzalloc(sizeof(*s) + smt_size * sizeof(struct smt_entry),
-		     GFP_KERNEL);
+	s = kvzalloc(struct_size(s, smtab, smt_size), GFP_KERNEL);
 	if (!s)
 		return NULL;
 	s->smt_size = smt_size;