mtd: nand: fix scan_read_raw_oob

It seems there is a bug in scan_read_raw_oob() in nand_bbt.c which
should cause wrong functioning of NAND_BBT_SCANALLPAGES option.

Artem: the patch did not apply and I had to amend it a bit.
Signed-off-by: NArtem Bityutskiy <artem.bityutskiy@linux.intel.com>
Cc: stable@kernel.org

drivers/mtd/nand/nand_bbt.c

@@ -324,6 +324,7 @@ static int scan_read_raw_oob(struct mtd_info *mtd, uint8_t *buf, loff_t offs,
 
 		buf += mtd->oobsize + mtd->writesize;
 		len -= mtd->writesize;
+		offs += mtd->writesize;
 	}
 	return 0;
 }