avfilter/vf_mcdeint: add missing "This file is part of FFmpeg"

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/vf_mcdeint.c

 /*
  * Copyright (c) 2006 Michael Niedermayer <michaelni@gmx.at>
  *
+ * This file is part of FFmpeg.
+ *
  * FFmpeg is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation; either version 2 of the License, or