mtd: gpmi: fix ECC regression

mtd: gpmi: fix ECC regression

The legacy ECC layout uses all the OOB area by computing the ECC
strength and ECC step size ourselves.

The patch "2febcdf mtd: gpmi: set the BCHs geometry with the ecc info"
makes the gpmi to use the ECC info (ECC strength and ECC step size)
provided by the MTD code, and creates a different NAND ECC layout
for the BCH, and use the new ECC layout. This causes a regression:

   We can not mount the ubifs which was created by the old NAND ECC layout.

This patch fixes this issue by reverting to the legacy ECC layout
firstly; if it fails, we try to use the new ECC layout.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>