ovl: filter of trusted xattr results in audit

When filtering xattr list for reading, presence of trusted xattr
results in a security audit log.  However, if there is other content
no errno will be set, and if there isn't, the errno will be -ENODATA
and not -EPERM as is usually associated with a lack of capability.
The check does not block the request to list the xattrs present.

Switch to ns_capable_noaudit to reflect a more appropriate check.

Signed-off-by: Mark Salyzyn <salyzyn@android.com>
Cc: linux-security-module@vger.kernel.org
Cc: kernel-team@android.com
Cc: stable@vger.kernel.org # v3.18+
Fixes: a082c6f6 ("ovl: filter trusted xattr for non-admin")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>