mtd: nand: use the nand_read_subpage index everywhere

Now that the index variable is correctly set earlier in this function
we can use it in other places that compute the same thing too.
Signed-off-by: Ron Lee <ron@debian.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/nand_base.c

@@ -1204,8 +1204,7 @@ static int nand_read_subpage(struct mtd_info *mtd, struct nand_chip *chip,
 	 * ecc.pos. Let's make sure that there are no gaps in ECC positions.
 	 */
 	for (i = 0; i < eccfrag_len - 1; i++) {
-		if (eccpos[i + start_step * chip->ecc.bytes] + 1 !=
-			eccpos[i + start_step * chip->ecc.bytes + 1]) {
+		if (eccpos[i + index] + 1 != eccpos[i + index + 1]) {
 			gaps = 1;
 			break;
 		}