[gnome-flashback] sound-applet: fix cast-function-type warning

[Alberts Muktupāvels <muktupavels src gnome org>]

commit 10abf948692affe0a5e898e67359cd5b77d41d35
Author: Alberts Muktupāvels <alberts muktupavels gmail com>
Date:   Sun Sep 9 01:09:08 2018 +0300

    sound-applet: fix cast-function-type warning

 gnome-flashback/libsound-applet/gvc-stream-status-icon.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/gnome-flashback/libsound-applet/gvc-stream-status-icon.c 
b/gnome-flashback/libsound-applet/gvc-stream-status-icon.c
index 1440257..f9bdffa 100644
--- a/gnome-flashback/libsound-applet/gvc-stream-status-icon.c
+++ b/gnome-flashback/libsound-applet/gvc-stream-status-icon.c
@@ -109,6 +109,13 @@ ungrab (GvcStreamStatusIcon *icon,
        gtk_widget_hide (icon->priv->dock);
 }
 
+static void
+show_all_cb (GtkWidget *widget,
+             gpointer   user_data)
+{
+  gtk_widget_show_all (widget);
+}
+
 static gboolean
 popup_dock (GvcStreamStatusIcon *icon,
             guint                time)
@@ -152,7 +159,7 @@ popup_dock (GvcStreamStatusIcon *icon,
         gdk_screen_get_monitor_geometry (screen, monitor_num, &monitor);
 
         gtk_container_foreach (GTK_CONTAINER (icon->priv->dock),
-                               (GtkCallback) gtk_widget_show_all, NULL);
+                               show_all_cb, NULL);
         gtk_widget_get_preferred_size (icon->priv->dock, &dock_req, NULL);
 
         if (orientation == GTK_ORIENTATION_VERTICAL) {