xfs: attribute scrub should use seen_enough to pass error values

When we're iterating all the attributes using the built-in xattr
iterator, we can use the seen_enough variable to pass error codes back
to the main scrub function instead of flattening them into 0/1.  This
will be used in a more exciting fashion in upcoming patches.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>