apparmor: put back designators in struct initialisers

Fixes: 8014370f

 ("apparmor: move path_link mediation to using labels")
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: John Johansen <john.johansen@canonical.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: James Morris <james.l.morris@oracle.com>