Clean compilar warnings

[unused-variable] warning removed from
    policyengine.c
    caipserver.c
    ocresource.c
[unused-but-set-variable] warning removed from
    psinterface.c
    policyengine.c
[return-type] warning removed from
    psinterface.c
[sign-compare] warning removed from
    doxmresource.c

Change-Id: I44b633871e78a2baf9d0595dff926834581160c9
Signed-off-by: George Nash <george.nash@intel.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10087
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Jon A. Cruz <jon@joncruz.org>