mtd: rawnand: sunxi: Fix the size of the last OOB region

The previous code assigned to the wrong structure member.

Fixes: c66811e ("mtd: nand: sunxi: switch to mtd_ooblayout_ops")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-By: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20221229181526.53766-6-samuel@sholland.org

Author: smaeul

drivers/mtd/nand/raw/sunxi_nand.c

@@ -1609,7 +1609,7 @@ static int sunxi_nand_ooblayout_free(struct mtd_info *mtd, int section,
 	if (section < ecc->steps)
 		oobregion->length = 4;
 	else
-		oobregion->offset = mtd->oobsize - oobregion->offset;
+		oobregion->length = mtd->oobsize - oobregion->offset;
 
 	return 0;
 }