mtd: sh_flctl: Fix hardware ECC behaviour

The flctl uses 10 bytes ECC data for every 512 bytes sector. This patch
makes the controller write all 40 bytes instead of 10 bytes only.

Signed-off-by: Bastian Hecht <hechtb@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>