avfilter/vf_yadif: fix "incompatible pointer type" warning

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_yadif.c

@@ -302,7 +302,7 @@ static void fixstride(AVFilterLink *link, AVFrame *f)
         return;
     av_frame_copy_props(dst, f);
     av_image_copy(dst->data, dst->linesize,
-                  f->data, f->linesize,
+                  (const uint8_t **)f->data, f->linesize,
                   dst->format, dst->width, dst->height);
     av_frame_unref(f);
     av_frame_move_ref(f, dst);