mtd: rawnand: marvell: 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>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/marvell_nand.c

@@ -2550,9 +2550,8 @@ static int marvell_nand_chip_init(struct device *dev, struct marvell_nfc *nfc,
 	}
 
 	/* Alloc the nand chip structure */
-	marvell_nand = devm_kzalloc(dev, sizeof(*marvell_nand) +
-				    (nsels *
-				     sizeof(struct marvell_nand_chip_sel)),
+	marvell_nand = devm_kzalloc(dev,
+				    struct_size(marvell_nand, sels, nsels),
 				    GFP_KERNEL);
 	if (!marvell_nand) {
 		dev_err(dev, "could not allocate chip structure\n");