ARM: integrator: impd1: 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 code was detected with the help of Coccinelle.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>

arch/arm/mach-integrator/impd1.c

@@ -390,7 +390,7 @@ static int __ref impd1_probe(struct lm_device *dev)
 			char *mmciname;
 
 			lookup = devm_kzalloc(&dev->dev,
-					      sizeof(*lookup) + 3 * sizeof(struct gpiod_lookup),
+					      struct_size(lookup, table, 3),
 					      GFP_KERNEL);
 			chipname = devm_kstrdup(&dev->dev, devname, GFP_KERNEL);
 			mmciname = devm_kasprintf(&dev->dev, GFP_KERNEL,