mtd: nand: jz4780: Update ecc correction error codes

Update jz4780_bch_ecc_correct's return codes with appropriate values,
as specified in /include/linux/mtd/nand.h.

Signed-off-by: Harvey Hunt <harvey.hunt@imgtec.com>
Cc: Alex Smith <alex@alex-smith.me.uk>
Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>