mtd: lpddr: 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: Boris Brezillon <bbrezillon@kernel.org>

drivers/mtd/lpddr/qinfo_probe.c

@@ -181,8 +181,8 @@ static struct lpddr_private *lpddr_probe_chip(struct map_info *map)
 	lpddr.numchips = 1;
 
 	numvirtchips = lpddr.numchips * lpddr.qinfo->HWPartsNum;
-	retlpddr = kzalloc(sizeof(struct lpddr_private) +
-			numvirtchips * sizeof(struct flchip), GFP_KERNEL);
+	retlpddr = kzalloc(struct_size(retlpddr, chips, numvirtchips),
+			   GFP_KERNEL);
 	if (!retlpddr)
 		return NULL;