mtd: at91: atmel_nand: return bit flips for the PMECC read_page()

This patch fix pmecc's read_page() to return maximum number of bitflips, 0 if uncorrectable.

In the commit: 3f91e94f ("mtd: nand: read_page() returns max_bitflips ()"),
The ecc.read_page() is changed to return the maximum number of bitflips.
And when meet uncorrectable bitflips it needs to return 0.

See the comment in nand.h:
 * @read_page:	function to read a page according to the ECC generator
 *		requirements; returns maximum number of bitflips corrected in
 *		any single ECC step, 0 if bitflips uncorrectable, -EIO hw error
Signed-off-by: Josh Wu <josh.wu@atmel.com>
Reviewed-by: Mike Dunn <mikedunn@newsguy.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>

drivers/mtd/nand/atmel_nand.c

@@ -723,6 +723,7 @@ static int pmecc_correction(struct mtd_info *mtd, u32 pmecc_stat, uint8_t *buf,
 	struct atmel_nand_host *host = nand_chip->priv;
 	int i, err_nbr, eccbytes;
 	uint8_t *buf_pos;
+	int total_err = 0;
 
 	eccbytes = nand_chip->ecc.bytes;
 	for (i = 0; i < eccbytes; i++)
@@ -750,12 +751,13 @@ static int pmecc_correction(struct mtd_info *mtd, u32 pmecc_stat, uint8_t *buf,
 				pmecc_correct_data(mtd, buf_pos, ecc, i,
 					host->pmecc_bytes_per_sector, err_nbr);
 				mtd->ecc_stats.corrected += err_nbr;
+				total_err += err_nbr;
 			}
 		}
 		pmecc_stat >>= 1;
 	}
 
-	return 0;
+	return total_err;
 }
 
 static int atmel_nand_pmecc_read_page(struct mtd_info *mtd,
@@ -767,6 +769,7 @@ static int atmel_nand_pmecc_read_page(struct mtd_info *mtd,
 	uint32_t *eccpos = chip->ecc.layout->eccpos;
 	uint32_t stat;
 	unsigned long end_time;
+	int bitflips = 0;
 
 	pmecc_writel(host->ecc, CTRL, PMECC_CTRL_RST);
 	pmecc_writel(host->ecc, CTRL, PMECC_CTRL_DISABLE);
@@ -789,11 +792,14 @@ static int atmel_nand_pmecc_read_page(struct mtd_info *mtd,
 	}
 
 	stat = pmecc_readl_relaxed(host->ecc, ISR);
-	if (stat != 0)
-		if (pmecc_correction(mtd, stat, buf, &oob[eccpos[0]]) != 0)
-			return -EIO;
-
+	if (stat != 0) {
+		bitflips = pmecc_correction(mtd, stat, buf, &oob[eccpos[0]]);
+		if (bitflips < 0)
+			/* uncorrectable errors */
 			return 0;
+	}
+
+	return bitflips;
 }
 
 static int atmel_nand_pmecc_write_page(struct mtd_info *mtd,