mtd: rawnand: fsl_upm: Use platform_get_resource() + devm_ioremap_resource()

Replace the of_address_to_resource() + devm_ioremap() calls by
platform_get_resource() + devm_ioremap_resource() ones which allows us
to get rid of one error message since devm_ioremap_resource() already
takes care of that.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200603134922.1352340-6-boris.brezillon@collabora.com