asrc_anullsrc: fix copyright

git blame says:
    109 Stefano Sabatini
      7 Clément Bœsch
      2 Reimar Döffinger
      2 Michael Niedermayer
      1 Reinhard Tartler
      1 Mans Rullgard

Initial commit:
commit 1ee410f3
Author: Stefano Sabatini <stefano.sabatini-lala@poste.it>
Date:   Sat Sep 25 01:56:58 2010 +0000

    Add asrc_anullsrc - null audio source.

    Based on a patch by "S.N. Hemanth Meenakshisundaram" smeenaks!ucsd!edu.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/asrc_anullsrc.c

 /*
+ * Copyright 2010 S.N. Hemanth Meenakshisundaram <smeenaks ucsd edu>
+ * Copyright 2010 Stefano Sabatini <stefano.sabatini-lala poste it>
+ *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or