selinux: small cleanups in selinux_audit_rule_init()

A few small tweaks to selinux_audit_rule_init():

- Adjust how we use the @rc variable so we are not doing any extra
  work in the common/success case.

- Related to the above, rework the 'out' jump label so that the
  success and error paths are different, simplifying both.

- Cleanup some of the vertical whitespace while we are making the
  other changes.

Signed-off-by: Paul Moore <paul@paul-moore.com>