mtd: rawnand: ams-delta: Stop using legacy .IOADDR_R/W

Replace use of legacy .IOADDR_R/W with runtime calculations based on
priv->io_base.

Suggested-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>