[gnome-builder] gui: fix -Wunused warning

[Christian Hergert <chergert src gnome org>]

commit 47548858e3d2237ccc08ea248cc6fe083f480ad2
Author: Christian Hergert <chergert redhat com>
Date:   Tue Feb 19 15:41:16 2019 -0800

    gui: fix -Wunused warning

 src/libide/gui/ide-workbench.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/libide/gui/ide-workbench.c b/src/libide/gui/ide-workbench.c
index 339ea0f32..b3e7887ca 100644
--- a/src/libide/gui/ide-workbench.c
+++ b/src/libide/gui/ide-workbench.c
@@ -633,7 +633,7 @@ ide_workbench_foreach_workspace (IdeWorkbench *self,
     {
       IdeWorkspace *workspace = iter->data;
       g_assert (IDE_IS_WORKSPACE (workspace));
-      callback (iter->data, user_data);
+      callback (GTK_WIDGET (workspace), user_data);
     }
 
   g_list_free (copy);