The error code returned by the ecc.correct() are not consistent over the
all implementations.

Document the expected behavior in include/linux/mtd/nand.h and fix
offending implementations.

[Brian: this looks like a bugfix for the ECC reporting in the bf5xx_nand
driver, but we haven't seen any testing results for it]
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>
Tested-by: NFranklin S Cooper Jr. <fcooper@ti.com>
Signed-off-by: NBrian Norris <computersforpeace@gmail.com>