[retro-gtk] doc: Add a missing private header

[Adrien Plazas <aplazas src gnome org>]

commit e3b29d027ec854d0478c2c51bda53d23df0e68a5
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Tue Oct 27 08:38:52 2020 +0100

    doc: Add a missing private header
    
    This fixes some compilation warnings.

 doc/meson.build | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/doc/meson.build b/doc/meson.build
index 0c0f7c84..3eff925d 100644
--- a/doc/meson.build
+++ b/doc/meson.build
@@ -7,6 +7,7 @@ docpath = get_option('datadir') / 'gtk-doc' / 'html'
 private_headers = [
   'ipc-runner-private.h',
   'retro-cairo-display-private.h',
+  'retro-controller-codes-private.h',
   'retro-controller-iterator-private.h',
   'retro-controller-state-private.h',
   'retro-core-view-controller-private.h',