mtd: rawnand: mxc: Convert to devm_platform_ioremap_resource()

Use devm_platform_ioremap_resource() to simplify code.

Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230707040622.78174-3-frank.li@vivo.com