cosmetics: Fix AltiVec spelling.

git-svn-id: file:///var/local/repositories/mplayer/trunk/libswscale@24685 b3059339-0415-0410-9bf9-f77b7e298cf2

yuv2rgb_altivec.c

 /*
   marc.hoffman@analog.com    March 8, 2004
 
-  Altivec Acceleration for Color Space Conversion revision 0.2
+  AltiVec acceleration for colorspace conversion revision 0.2
 
   convert I420 YV12 to RGB in various formats,
     it rejects images that are not in 420 formats