virt-host-validate: Fix build on non-Linux

For non-Linux platforms we have
virHostValidateCGroupControllers() stub which only reports an
error. But we are not marking the ignored arguments the way we
should.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>

tools/virt-host-validate-common.c

@@ -322,8 +322,8 @@ int virHostValidateCGroupControllers(const char *hvname,
     return ret;
 }
 #else /*  !__linux__ */
-int virHostValidateCGroupControllers(const char *hvname,
-                                     int controllers,
+int virHostValidateCGroupControllers(const char *hvname ATTRIBUTE_UNUSED,
+                                     int controllers ATTRIBUTE_UNUSED,
                                      virHostValidateLevel level)
 {
     virHostMsgFail(level, "%s", "This platform does not support cgroups");