mtd: rawnand: cadence: fix the calculation of the avaialble OOB size

The value of cdns_chip->sector_count is not known at the moment
of the derivation of ecc_size, leading to a zero value. Fix
this by assigning ecc_size later in the code.

Fixes: ec4ba01e ("mtd: rawnand: Add new Cadence NAND driver to MTD subsystem")
Cc: stable@vger.kernel.org
Signed-off-by: Piotr Sroka <piotrs@cadence.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1581328530-29966-2-git-send-email-piotrs@cadence.com