mtd: rawnand: onfi: Avoid doing a copy of the parameter page

There is no need for copying the parameter page, playing with
pointers does the trick.

There is not functional change.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200428094302.14624-7-miquel.raynal@bootlin.com