mtd: atmel_nand: using a stronger ECC is not dangerous

We don't have to issue a warning when a stronger error correcting
capability is chosen.

Signed-off-by: Richard Genoud <richard.genoud@gmail.com>
Acked-by: Josh Wu <josh.wu@atmel.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>