fix affs parse_options()

Error handling in that sucker got broken back in 2003.  If function
returns 0 on failure, it's not nice to add return -EINVAL into it.
Adding return 1 on other failure exits is also not a good thing (and
yes, original success exits with 1 and some of failure exits with 0
are still there; so's the original logics in callers).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>