float_dsp.c: Restore author attribution that was removed by libav while moving code to libavutil

Original code comes from:
commit eb4825b5d4
Author: Loren Merritt <lorenm@u.washington.edu>
Date:   Thu Aug 10 19:06:25 2006 +0000

    sse and 3dnow implementations of float->int conversion and mdct windowing.
    15% faster vorbis.

and

commit 0bde73d907
Author: Michael Niedermayer <michaelni@gmx.at>
Date:   Tue May 17 19:02:43 2005 +0000

    Vorbis decoder by (Balatoni Denes | dbalatoni programozo hu)

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/float_dsp.c

@@ -1,18 +1,21 @@
 /*
- * This file is part of Libav.
+ * Copyright 2005 Balatoni Denes
+ * Copyright 2006 Loren Merritt
  *
- * Libav is free software; you can redistribute it and/or
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
- * Libav is distributed in the hope that it will be useful,
+ * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
- * License along with Libav; if not, write to the Free Software
+ * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */