apparmor: Replace spin_is_locked() with lockdep

lockdep_assert_held() is better suited to checking locking requirements,
since it won't get confused when someone else holds the lock. This is
also a step towards possibly removing spin_is_locked().

Signed-off-by: Lance Roy <ldr709@gmail.com>
Cc: John Johansen <john.johansen@canonical.com>
Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: <linux-security-module@vger.kernel.org>
Signed-off-by: John Johansen <john.johansen@canonical.com>