mtd: onenand: simplify the return expression of onenand_transfer_auto_oob

Simplify the return expression.

Signed-off-by: Liu Shixin <liushixin2@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200921082441.2591669-1-liushixin2@huawei.com