mtd: rawnand: export 'nand_exit_status_op()'

Export this function to work in pair with 'nand_status_op()' which is
already exported.

Signed-off-by: Arseniy Krasnov <AVKrasnov@sberdevices.ru>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230705104403.696680-2-AVKrasnov@sberdevices.ru