keep in sync with dsputil, makes --disable-decoder=vorbis build

Originally committed as revision 5979 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/ppc/dsputil_altivec.c

@@ -1854,5 +1854,7 @@ void dsputil_init_altivec(DSPContext* c, AVCodecContext *avctx)
 
     c->hadamard8_diff[0] = hadamard8_diff16_altivec;
     c->hadamard8_diff[1] = hadamard8_diff8x8_altivec;
+#ifdef CONFIG_VORBIS_DECODER
     c->vorbis_inverse_coupling = vorbis_inverse_coupling_altivec;
+#endif
 }