mtd: rawnand: timings: Make onfi_fill_interface_config() a void helper

Warn the user if the parameters are wrong but basically it would mean
there is a serious issue in the NAND core. So no need to ever check
its output, let's make this helper return void.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200529111322.7184-21-miquel.raynal@bootlin.com