mtd: nand: s3c2410: kill the ->ecc_layout field

The s3c2410 is allowing board data to overload the default ECC layout
defined inside the driver, but this feature is not used by board
specific definitions.
Kill this field so that we can easily move to a model where ecclayout
are dynamically allocated by the NAND controller driver.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>