apparmor: fix undefined reference to `aa_g_hash_policy'

The kernel build bot turned up a bad config combination when
CONFIG_SECURITY_APPARMOR is y and CONFIG_SECURITY_APPARMOR_HASH is n,
resulting in the build error
   security/built-in.o: In function `aa_unpack':
   (.text+0x841e2): undefined reference to `aa_g_hash_policy'

Signed-off-by: John Johansen <john.johansen@canonical.com>