[gnome-devel-docs] Fix function declaration that breaks the build

[David King <davidk src gnome org>]

commit aead9010ba742ff777eea6253851a42dfd09f142
Author: Luis Menina <liberforce freeside fr>
Date:   Wed Apr 17 09:02:16 2019 +0000

    Fix function declaration that breaks the build

 platform-demos/C/samples/scale.c | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/platform-demos/C/samples/scale.c b/platform-demos/C/samples/scale.c
index 5550f9ed..6b4d5978 100644
--- a/platform-demos/C/samples/scale.c
+++ b/platform-demos/C/samples/scale.c
@@ -32,6 +32,7 @@ hscale_moved (GtkRange *range,
  * reacts to the signal. It does the same thing as the function above, except with
  * the vertical scale.
  */
+static void
 vscale_moved (GtkRange *range,
               gpointer  user_data)
 {