powerpc/ps3: Use struct_size() in 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 = kzalloc(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 = kzalloc(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: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/ps3/device-init.c

@@ -354,9 +354,7 @@ static int ps3_setup_storage_dev(const struct ps3_repository_device *repo,
 		 repo->dev_index, repo->dev_type, port, blk_size, num_blocks,
 		 num_regions);
 
-	p = kzalloc(sizeof(struct ps3_storage_device) +
-		    num_regions * sizeof(struct ps3_storage_region),
-		    GFP_KERNEL);
+	p = kzalloc(struct_size(p, regions, num_regions), GFP_KERNEL);
 	if (!p) {
 		result = -ENOMEM;
 		goto fail_malloc;