rdft: Move some variables into a separate block

This avoids an unused variable warning with hardcoded tables.

libavcodec/rdft.c

@@ -99,8 +99,6 @@ static void rdft_calc_c(RDFTContext *s, FFTSample *data)
 av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
 {
     int n = 1 << nbits;
-    int i;
-    const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1)*2*M_PI/n;
 
     s->nbits           = nbits;
     s->inverse         = trans == IDFT_C2R || trans == DFT_C2R;
@@ -116,7 +114,10 @@ av_cold int ff_rdft_init(RDFTContext *s, int nbits, enum RDFTransformType trans)
     s->tcos = ff_cos_tabs[nbits];
     s->tsin = ff_sin_tabs[nbits]+(trans == DFT_R2C || trans == DFT_C2R)*(n>>2);
 #if !CONFIG_HARDCODED_TABLES
-    for (i = 0; i < (n>>2); i++) {
+    {
+        int i;
+        const double theta = (trans == DFT_R2C || trans == DFT_C2R ? -1 : 1) * 2 * M_PI / n;
+        for (i = 0; i < (n >> 2); i++)
             s->tsin[i] = sin(i * theta);
     }
 #endif