mtd: rawnand: micron: Update ecc_stats.corrected

Even if we can't update ecc_stats.corrected with an accurate value we
should at least increase the number of bitflips so that MTD users can
know that there was some bitflips.

Just add chip->ecc.strength to mtd->ecc_stats.corrected which should
account for the worst case situation.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>