Fix compilation on PPC 470.

Originally committed as revision 22584 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/h264dsp.c

@@ -315,6 +315,6 @@ void ff_h264dsp_init(H264DSPContext *c)
     c->h264_loop_filter_strength= NULL;
 
     if (ARCH_ARM) ff_h264dsp_init_arm(c);
-    if (ARCH_PPC) ff_h264dsp_init_ppc(c);
+    if (HAVE_ALTIVEC) ff_h264dsp_init_ppc(c);
     if (HAVE_MMX) ff_h264dsp_init_x86(c);
 }