[mutter] Shut up some compiler warnings

[Florian Müllner <fmuellner src gnome org>]

commit 72d6efc0d52cbba4d7eff8c7e7cb940bb435a964
Author: Florian Müllner <fmuellner gnome org>
Date:   Thu Jan 21 17:10:01 2016 +0100

    Shut up some compiler warnings

 src/wayland/meta-wayland-data-device.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/src/wayland/meta-wayland-data-device.c b/src/wayland/meta-wayland-data-device.c
index d5b4c06..b0652a0 100644
--- a/src/wayland/meta-wayland-data-device.c
+++ b/src/wayland/meta-wayland-data-device.c
@@ -213,7 +213,7 @@ struct wl_array *
 meta_wayland_data_source_get_mime_types (const MetaWaylandDataSource *source)
 {
   MetaWaylandDataSourcePrivate *priv =
-    meta_wayland_data_source_get_instance_private (source);
+    meta_wayland_data_source_get_instance_private ((MetaWaylandDataSource *)source);
 
   return &priv->mime_types;
 }
@@ -1461,7 +1461,7 @@ meta_wayland_data_source_has_mime_type (const MetaWaylandDataSource *source,
                                         const gchar                 *mime_type)
 {
   MetaWaylandDataSourcePrivate *priv =
-    meta_wayland_data_source_get_instance_private (source);
+    meta_wayland_data_source_get_instance_private ((MetaWaylandDataSource *)source);
   gchar **p;
 
   wl_array_for_each (p, &priv->mime_types)