ramips: correct page read return value of the mt7621 nand driver

read_page() need to return maximum number of bitflips instead of the
accumulated number. Change takes from upstream mt7621 u-boot [1].

 * @read_page:  function to read a page according to the ECC generator
 *              requirements; returns maximum number of bitflips
 *              corrected in any single ECC step, -EIO hw error

[1] https://lore.kernel.org/all/cover.1653015383.git.weijie.gao@mediatek.com/

Signed-off-by: Shiji Yang <yangshiji66@qq.com>

target/linux/ramips/files/drivers/mtd/nand/raw/mt7621_nand.c

@@ -1006,7 +1006,7 @@ static int mt7621_nfc_read_page_hwecc(struct nand_chip *nand, uint8_t *buf,
 {
 	struct mt7621_nfc *nfc = nand_get_controller_data(nand);
 	struct mtd_info *mtd = nand_to_mtd(nand);
-	int bitflips = 0;
+	int bitflips = 0, ret = 0;
 	int rc, i;
 
 	nand_read_page_op(nand, page, 0, NULL, 0);
@@ -1031,7 +1031,7 @@ static int mt7621_nfc_read_page_hwecc(struct nand_chip *nand, uint8_t *buf,
 		mt7621_nfc_read_sector_fdm(nfc, i);
 
 		if (rc < 0) {
-			bitflips = -EIO;
+			ret = -EIO;
 			continue;
 		}
 
@@ -1043,10 +1043,11 @@ static int mt7621_nfc_read_page_hwecc(struct nand_chip *nand, uint8_t *buf,
 			dev_dbg(nfc->dev,
 				 "Uncorrectable ECC error at page %d.%d\n",
 				 page, i);
-			bitflips = -EBADMSG;
+			bitflips = nand->ecc.strength + 1;
 			mtd->ecc_stats.failed++;
-		} else if (bitflips >= 0) {
-			bitflips += rc;
+		} else {
+			if (rc > bitflips)
+				bitflips = rc;
 			mtd->ecc_stats.corrected += rc;
 		}
 	}
@@ -1055,6 +1056,9 @@ static int mt7621_nfc_read_page_hwecc(struct nand_chip *nand, uint8_t *buf,
 
 	nfi_write16(nfc, NFI_CON, 0);
 
+	if (ret < 0)
+		return ret;
+
 	return bitflips;
 }