Do not initialize ff_cos_* tables again in rdft_init, they are already

initialized by ff_fft_init and using different code can result in slightly
different values, in addition it crashes when the tables are hardcoded.
On amd64 this slightly changes qdm2 output.

Originally committed as revision 20237 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/dsputil.h

@@ -840,7 +840,7 @@ typedef struct {
     int sign_convention;
 
     /* pre/post rotation tables */
-    FFTSample *tcos;
+    const FFTSample *tcos;
     FFTSample *tsin;
     FFTContext fft;
 } RDFTContext;

libavcodec/rdft.c

@@ -64,7 +64,6 @@ av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
     s->tcos = ff_cos_tabs[nbits-4];
     s->tsin = ff_sin_tabs[nbits-4]+(trans == RDFT || trans == IRIDFT)*(n>>2);
     for (i = 0; i < (n>>2); i++) {
-        s->tcos[i] = cos(i*theta);
         s->tsin[i] = sin(i*theta);
     }
     return 0;