ima: Do not audit if CONFIG_INTEGRITY_AUDIT is not set

If Integrity is not auditing, IMA shouldn't audit, either.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>