avfilter/vf_transpose: Fix regression with packed pixel formats

Regression since: c6939f65Found-by: Paul B Mahol <onemda@gmail.com>
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/vf_transpose.c

@@ -217,7 +217,7 @@ static int config_props_output(AVFilterLink *outlink)
 
     s->hsub = desc_in->log2_chroma_w;
     s->vsub = desc_in->log2_chroma_h;
-    s->planes = desc_in->nb_components;
+    s->planes = av_pix_fmt_count_planes(outlink->format);
 
     av_assert0(desc_in->nb_components == desc_out->nb_components);