mqtt: Fix pedantic enum warning

src/apps/mqtt/mqtt.c:81:17: error: comma at end of enumerator list [-Werror=pedantic]
diff --git a/src/apps/mqtt/mqtt.c b/src/apps/mqtt/mqtt.c
index cd271b1..5f4a9ef 100644
--- a/src/apps/mqtt/mqtt.c
+++ b/src/apps/mqtt/mqtt.c
@@ -78,7 +78,7 @@
   TCP_DISCONNECTED,
   TCP_CONNECTING,
   MQTT_CONNECTING,
-  MQTT_CONNECTED,
+  MQTT_CONNECTED
 };
 
 /**