mtd: rawnand: sunxi: Embed sunxi_nand_hw_ecc by value

The sunxi_nand_hw_ecc object is not shared, and it has the same lifetime
as the sunxi_nand_chip which points to it, so we can embed it in the
outer structure instead of using a pointer. This removes an unnecessary
memory allocation and simplifies the error handling code.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230204143520.9682-3-samuel@sholland.org