Fix compiler warning about unused variables.

modules/video_filter/croppadd.c

@@ -55,7 +55,6 @@ vlc_module_end();
 static int OpenFilter( vlc_object_t *p_this )
 {
     filter_t *p_filter = (filter_t*)p_this;
-    filter_sys_t *p_sys;
 
     if( p_filter->fmt_in.video.i_chroma != p_filter->fmt_out.video.i_chroma )
     {
@@ -82,6 +81,7 @@ static int OpenFilter( vlc_object_t *p_this )
  *****************************************************************************/
 static void CloseFilter( vlc_object_t *p_this )
 {
+    VLC_UNUSED(p_this);
 }
 
 /****************************************************************************