mtd: gpmi: fix the wrong DMA command.

The last DMA command of ECC read page is used to disable the BCH module.
But the original code missed to set the pio[2] which is used to set the
GPMI_HW_GPMI_ECCCTRL register. fix it now.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>