mtd: rawnand: cs553x: Stop using chip->legacy.IO_ADDR_{R, W}

Now that we have our own controller struct we can keep the MMIO pointer
in there and use instead of using the chip->legacy.IO_ADDR_{R,W} fields.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200501090650.1138200-3-boris.brezillon@collabora.com