mtd: rawnand: meson: use struct_size macro

Use the recently introduced struct_size macro instead of open-coding
it's logic.
No functional changes.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Tested-by:Liang Yang <liang.yang@amlogic.com>
Acked-by: Liang Yang <liang.yang@amlogic.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/meson_nand.c

@@ -1242,8 +1242,7 @@ meson_nfc_nand_chip_init(struct device *dev,
 		return -EINVAL;
 	}
 
-	meson_chip = devm_kzalloc(dev,
-				  sizeof(*meson_chip) + (nsels * sizeof(u8)),
+	meson_chip = devm_kzalloc(dev, struct_size(meson_chip, sels, nsels),
 				  GFP_KERNEL);
 	if (!meson_chip)
 		return -ENOMEM;