mtd: rawnand: marvell: Rename a function to clarify

Cosmetic change to clarify the purpose of the function.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200424164501.26719-6-miquel.raynal@bootlin.com