mtd: nand: jz4780: Use mtd_set_ooblayout() to set the ooblayout

The mtd_set_ooblayout() accesor has been added to hide internals of
mtd_info and ease future refactoring. Call mtd_set_ooblayout() instead of
directly accessing mtd->ooblayout.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Harvey Hunt <harveyhuntnexus@gmail.com>