memory: atmel-ebi: 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;
        void *entry[];
};

instance = devm_kzalloc(dev, sizeof(struct foo) + sizeof(void *) * count, 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 issue was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>

drivers/memory/atmel-ebi.c

@@ -327,8 +327,7 @@ static int atmel_ebi_dev_setup(struct atmel_ebi *ebi, struct device_node *np,
 		return -EINVAL;
 	}
 
-	ebid = devm_kzalloc(ebi->dev,
-			    sizeof(*ebid) + (numcs * sizeof(*ebid->configs)),
+	ebid = devm_kzalloc(ebi->dev, struct_size(ebid, configs, numcs),
 			    GFP_KERNEL);
 	if (!ebid)
 		return -ENOMEM;