[gnome-control-center] printers: Fix warning about wrong data type

[Felipe Borges <felipeborges src gnome org>]

commit 3f5bc8369b79e5434437bc483ea89e3024b0c5e2
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Jun 26 15:57:20 2018 +1200

    printers: Fix warning about wrong data type

 panels/printers/pp-new-printer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/panels/printers/pp-new-printer.c b/panels/printers/pp-new-printer.c
index cc0d259ab..e1e480817 100644
--- a/panels/printers/pp-new-printer.c
+++ b/panels/printers/pp-new-printer.c
@@ -1140,7 +1140,7 @@ DBus method \"MissingExecutables\" to find missing executables and filters.");
       data->executables = executables;
 
       item = data->executables;
-      g_dbus_connection_call (g_object_ref (source_object),
+      g_dbus_connection_call (g_object_ref (G_DBUS_CONNECTION (source_object)),
                               PACKAGE_KIT_BUS,
                               PACKAGE_KIT_PATH,
                               PACKAGE_KIT_QUERY_IFACE,