mtd: nand: make nand_ooblayout_lp_hamming_ops static

nand_ooblayout_lp_hamming_ops can be made static as it does not need to be
in global scope.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>