mtd: rawnand: mxc: Use device_get_match_data()

The retrieval of driver data can be a bit simplified by using
device_get_match_data(), so switch to it.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201204145818.32739-1-festevam@gmail.com