mtd: rawnand: Fix nand_setup_data_interface() description

This is a copy/paste error and belongs to nand_init_data_interface()
description.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200529111322.7184-11-miquel.raynal@bootlin.com