mtd: rawnand: Avoid accessing NV-DDR timings from legacy code

Legacy code should not benefit from newer features, especially in
helpers that have been deprecated for a very long time. People who want
NV-DDR support must migrate their driver to the ->exec_op() API.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210505213750.257417-13-miquel.raynal@bootlin.com