cosmetics: Fix AltiVec spelling.

Originally committed as revision 24685 to svn://svn.mplayerhq.hu/mplayer/trunk/libswscale

libswscale/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