mtd: cfi: cmdset_0001: Use struct_size() in kmalloc()

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 = kmalloc(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 = kmalloc(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: Boris Brezillon <bbrezillon@kernel.org>

drivers/mtd/chips/cfi_cmdset_0001.c

@@ -756,7 +756,8 @@ static int cfi_intelext_partition_fixup(struct mtd_info *mtd,
 		}
 
 		numvirtchips = cfi->numchips * numparts;
-		newcfi = kmalloc(sizeof(struct cfi_private) + numvirtchips * sizeof(struct flchip), GFP_KERNEL);
+		newcfi = kmalloc(struct_size(newcfi, chips, numvirtchips),
+				 GFP_KERNEL);
 		if (!newcfi)
 			return -ENOMEM;
 		shared = kmalloc_array(cfi->numchips,