mtd: rawnand: atmel: Fix spelling mistake in error message

Wrong copy/paste from the previous block, the error message should
refer to #size-cells instead of #address-cells.

Fixes: f88fc122 ("mtd: nand: Cleanup/rework the atmel_nand driver")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>