[gnome-control-center] network: Fix small memory leak

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 4ba3a2c3d1ca8d614610f6c17d39dd3b9b98da95
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Oct 1 12:51:55 2019 +1300

    network: Fix small memory leak

 panels/network/net-device-ethernet.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/panels/network/net-device-ethernet.c b/panels/network/net-device-ethernet.c
index 86c87ab30..7a43f4fcd 100644
--- a/panels/network/net-device-ethernet.c
+++ b/panels/network/net-device-ethernet.c
@@ -203,7 +203,7 @@ device_ethernet_refresh_ui (NetDeviceEthernet *device)
         NMDevice *nm_device;
         NMDeviceState state;
         GtkWidget *widget;
-        gchar *speed = NULL;
+        g_autofree gchar *speed = NULL;
 
         nm_device = net_device_get_nm_device (NET_DEVICE (device));