fix compile warning when meson build

- Fix compile warning:
  [-Werror=unused-variable], [-Werror=sign-compare] and
  deprecated INSTANTIATE_TEST_CASE_P

Signed-off-by: Harvey.Wu <Harvey.Wu@quantatw.com>
Change-Id: If8713f0b938cd5306bbe19a9078731db0c3667dc
diff --git a/dbus/dbuspassive.cpp b/dbus/dbuspassive.cpp
index 182a9a5..41047a1 100644
--- a/dbus/dbuspassive.cpp
+++ b/dbus/dbuspassive.cpp
@@ -331,7 +331,8 @@
     return 0;
 }
 
-int dbusHandleSignal(sd_bus_message* msg, void* usrData, sd_bus_error* err)
+int dbusHandleSignal(sd_bus_message* msg, void* usrData,
+                     [[maybe_unused]] sd_bus_error* err)
 {
     auto sdbpMsg = sdbusplus::message_t(msg);
     DbusPassive* obj = static_cast<DbusPassive*>(usrData);