audit: remove the BUG() calls in the audit rule comparison functions

The audit_data_to_entry() function ensures that the operator is valid
so we can get rid of these BUG() calls.  We keep the "return 0" just
so the system behaves in a sane-ish manner should something go
horribly wrong.

Signed-off-by: Paul Moore <paul@paul-moore.com>
Acked-by: Richard Guy Briggs <rgb@redhat.com>