mtd: spinand: Fix MTD_OPS_AUTO_OOB requests

The initial change breaking the logic is
commit 3d1f08b0 ("mtd: spinand: Use the external ECC engine logic")
It inadvertently dropped proper OOB support while doing something
else.

Shortly later, half of it got re-integrated by
commit 868cbe2a ("mtd: spinand: Fix OOB read")
(pointing by the way to a  more early change which had nothing to do
with the issue). Problem is, this commit failed to revert the faulty
change entirely and missed the logic handling MTD_OPS_AUTO_OOB
requests.

Let's fix this mess by re-inserting the missing part now.

Fixes: 868cbe2a ("mtd: spinand: Fix OOB read")
Reported-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210107083813.24283-1-miquel.raynal@bootlin.com