avformat/dump: put copyright back from the file from which dump.c was split out

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

libavformat/dump.c

 /*
  * Various pretty-printing functions for use within FFmpeg
+ * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
  *
  * This file is part of FFmpeg.
  *