mtd: nand: ecc-hamming: Populate the public nsteps field

Advertize the actual number of steps that will actually be used by the
driver by populating the public field.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Tested-by: Adam Ford <aford173@gmail.com> #logicpd Torpedo
Link: https://lore.kernel.org/linux-mtd/20210127203020.9574-4-miquel.raynal@bootlin.com