treewide: Use DBus defines instead of direct string literals

While cleaning up the BlueZ counterpart of strings defined in
preprocessor macros it is only consistent to take care of all DBUS_
macros as a whole.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/477>

src/pulsecore/rtkit.c

@@ -77,7 +77,7 @@ static long long rtkit_get_int_property(DBusConnection *connection, const char*
         if (!(m = dbus_message_new_method_call(
                               RTKIT_SERVICE_NAME,
                               RTKIT_OBJECT_PATH,
-                              "org.freedesktop.DBus.Properties",
+                              DBUS_INTERFACE_PROPERTIES,
                               "Get"))) {
                 ret = -ENOMEM;
                 goto finish;