mtd: gpmi: Always report ECC stats and return max_bitflips

Always report corrected and failed ECC stats back up to the MTD layer.  Also
return max_bitflips from read_page() as is expected from NAND drivers now.

Signed-off-by: Zach Sadecki <zsadecki@itwatchdogs.com>
Acked-by: Huang Shijie <b32955@freescale.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>