nand_device embeds a nand_ecc_req object which contains the minimum
strength and step-size required by the NAND device.

Drop the chip->ecc_{strength,step}_ds fields and use
chip->base.eccreq.{strength,step_size} instead.
Signed-off-by: NBoris Brezillon <bbrezillon@kernel.org>
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: NFrieder Schrempf <frieder.schrempf@kontron.de>