Remove unused variable from wma_decode_block() found by CSA.

Originally committed as revision 18568 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/wmadec.c

@@ -683,9 +683,8 @@ static int wma_decode_block(WMACodecContext *s)
 
 next:
     for(ch = 0; ch < s->nb_channels; ch++) {
-        int n4, index, n;
+        int n4, index;
 
-        n = s->block_len;
         n4 = s->block_len / 2;
         if(s->channel_coded[ch]){
             ff_imdct_calc(&s->mdct_ctx[bsize], s->output, s->coefs[ch]);