staging: mt29f_spinand: set ECC algorithm explicitly

This is part of process deprecating NAND_ECC_SOFT_BCH (and switching to
enum nand_ecc_algo).

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>