bluray: Fixing a warning

Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
(cherry picked from commit 091a42674c70a913fab99d868a7e37ea0eb0d2b0)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/access/bluray.c

@@ -421,7 +421,7 @@ static int blurayControl(demux_t *p_demux, int query, va_list args)
 
         case DEMUX_GET_META:
         {
-            struct meta_dl *meta = bd_get_meta(p_sys->bluray);
+            const struct meta_dl *meta = bd_get_meta(p_sys->bluray);
             if(!meta)
                 return VLC_EGENERIC;