mxs_nand: Fix ECC strength for NAND flash with OOB size of 224

mxs_nand: Fix ECC strength for NAND flash with OOB size of 224

On a board with an i.mx28 and a Micron MT29F4G08ABAEAH4, Linux says:

NAND device: Manufacturer ID: 0x2c, Chip ID: 0xdc (Micron MT29F4G08ABAEAH4),
512MiB, page size: 4096, OOB size: 224) the ECC strength is 16.

root@(none):/sys/devices/virtual/mtd/mtd0# for i in ecc_strength oobsize subpagesize; do echo $i = `cat $i`; done
ecc_strength = 16
oobsize = 224
subpagesize = 4096

The ECC strength was not properly discovered by U-Boot causing the data
written by Linux to return an -74 (EBADMSG) when read from U-Boot. This
patch fixes mxs_nand_get_ecc_strength() to function in case of a NAND
flash with page_data_size = 4096 and page_oob_size= 224.

Signed-off-by: Elie De Brauwer <eliedebrauwer@gmail.com>
Acked-by: Scott Wood <scottwood@freescale.com>