net: hns: Use struct_size() in devm_kzalloc()

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 = devm_kzalloc(dev, 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 = devm_kzalloc(dev, struct_size(instance, entry, count), GFP_KERNEL);

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/hisilicon/hns/hns_dsaf_rcb.c

@@ -788,8 +788,9 @@ int hns_rcb_common_get_cfg(struct dsaf_device *dsaf_dev,
 	int ring_num = hns_rcb_get_ring_num(dsaf_dev);
 
 	rcb_common =
-		devm_kzalloc(dsaf_dev->dev, sizeof(*rcb_common) +
-			ring_num * sizeof(struct ring_pair_cb), GFP_KERNEL);
+		devm_kzalloc(dsaf_dev->dev,
+			     struct_size(rcb_common, ring_pair_cb, ring_num),
+			     GFP_KERNEL);
 	if (!rcb_common) {
 		dev_err(dsaf_dev->dev, "rcb common devm_kzalloc fail!\n");
 		return -ENOMEM;