mtd: nand: Base BCH ECC bytes on required strength

NAND devices with page sizes over 4 KiB require more than 4-bits of ECC
coverage. This patch calculates the value of ecc_bytes based on a still
assumed 512-byte step size (13-bits) and the ecc_strength.

Example:
Micron M73A devices (8 KiB page) require 8-bit ECC per 512-byte
Signed-off-by: Jordan Friendshuh <jfriendshuh@xes-inc.com>
Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/nand_base.c

@@ -4035,7 +4035,7 @@ int nand_scan_tail(struct mtd_info *mtd)
 		 */
 		if (!ecc->size && (mtd->oobsize >= 64)) {
 			ecc->size = 512;
-			ecc->bytes = 7;
+			ecc->bytes = DIV_ROUND_UP(13 * ecc->strength, 8);
 		}
 		ecc->priv = nand_bch_init(mtd, ecc->size, ecc->bytes,
 					       &ecc->layout);