Fixed FTBFS on Debian/Testing due to const conversion error.

diff --git a/tdenetworkmanager/src/tdenetman-wireless_device_tray.cpp b/tdenetworkmanager/src/tdenetman-wireless_device_tray.cpp
index 4108be6..a3a4b4c 100644
--- a/tdenetworkmanager/src/tdenetman-wireless_device_tray.cpp
+++ b/tdenetworkmanager/src/tdenetman-wireless_device_tray.cpp
@@ -198,7 +198,7 @@
 			continue;
 		}
 
-		TDEWiFiConnection* wireless = dynamic_cast<const TDEWiFiConnection*>(*it);
+		const TDEWiFiConnection* wireless = dynamic_cast<const TDEWiFiConnection*>(*it);
 
 		if (!wireless) {
 			continue;