x86/dsputil: Fix author attribution after code has been moved/splited around

Reference:
commit 3615e2be
Author: Michael Niedermayer <michaelni@gmx.at>
Date:   Tue Dec 2 22:02:57 2003 +0000

    h263_h_loop_filter_mmx

    Originally committed as revision 2553 to svn://svn.ffmpeg.org/ffmpeg/trunk

commit 359f98de
Author: Michael Niedermayer <michaelni@gmx.at>
Date:   Tue Dec 2 20:28:10 2003 +0000

    h263_v_loop_filter_mmx

    Originally committed as revision 2552 to svn://svn.ffmpeg.org/ffmpeg/trunkSigned-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/x86/dsputil.asm

 ;******************************************************************************
 ;* MMX optimized DSP utils
 ;* Copyright (c) 2008 Loren Merritt
+;* Copyright (c) 2003-2013 Michael Niedermayer
+;* Copyright (c) 2013 Daniel Kang
 ;*
 ;* This file is part of FFmpeg.
 ;*