The calculation of readtotal must be bit alligend. If not the bch core
finds bit flips in every page, because readtotal is too small.
This bug was mostly introduced since commit "51061a9 mtd: nand: nand_mxs:
Add subpage read support".

Tested with:
nand: NAND device: Manufacturer ID: 0x01, Chip ID: 0xd3 (AMD/Spansion
S34ML08G2), 1024MiB, page size: 2048, OOB size: 128

nand: NAND device: Manufacturer ID: 0x2c, Chip ID: 0xdc (Micron
MT29F4G08ABADAWP), 512MiB, page size: 2048, OOB size: 64

nand: NAND device: Manufacturer ID: 0xec, Chip ID: 0xd3 (Samsung NAND
1GiB 3,3V 8-bit), 1024MiB, page size: 2048, OOB size: 64

Signed-off-by: Christian Hemp <c.hemp@phytec.de>
Signed-off-by: Stefan Lengfeld <s.lengfeld@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>