lavfi/avcodec.c: fix copyright

git blame:
     45 Stefano Sabatini
     23 Clément Bœsch
      4 Michael Niedermayer
      3 Robert Nagy
      3 Nicolas George
      2 Roger Pau Monné

Initial commit:
commit 566666ca
Author: Stefano Sabatini <stefano.sabatini-lala@poste.it>
Date:   Sun May 1 14:47:05 2011 +0200
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/avcodec.c

 /*
+ * Copyright 2011 Stefano Sabatini | stefasab at gmail.com
+ *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or