mtd: onenand: s3c6410: Notify upper layer about corrected ECC errors

This patch corrects s3c6410_onenand_wait() to return -EUCLEAN error code
if a correctable ECC error occurs, to allow memory users such as UBIFS
handle such cases according to their policies.

Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>