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Merges the FFT scaling with the MDCT pre-rotate

--- a/celt/mdct.c

+++ b/celt/mdct.c

@@ -182,20 +182,27 @@

       for(i=0;i<N4;i++)

       {

          kiss_fft_cpx yc;

+         kiss_twiddle_scalar t0, t1;

          kiss_fft_scalar re, im, yr, yi;

+         t0 = t[i<<shift];

+         t1 = t[(N4-i)<<shift];

+#ifdef FIXED_POINT

+         t0 = MULT16_16_P15(t0, scale);

+         t1 = MULT16_16_P15(t1, scale);

+#else

+         t0 *= st->scale;

+         t1 *= st->scale;

+#endif

          re = *yp++;

          im = *yp++;

-         yr = -S_MUL(re,t[i<<shift])  -  S_MUL(im,t[(N4-i)<<shift]);

-         yi = -S_MUL(im,t[i<<shift])  +  S_MUL(re,t[(N4-i)<<shift]);

+         yr = -S_MUL(re,t0)  -  S_MUL(im,t1);

+         yi = -S_MUL(im,t0)  +  S_MUL(re,t1);

          /* works because the cos is nearly one */

          yc.r = yr + S_MUL(yi,sine);

          yc.i = yi - S_MUL(yr,sine);

 #ifdef FIXED_POINT

-         yc.r = SHR32(MULT16_32_Q15(scale, yc.r), scale_shift);

-         yc.i = SHR32(MULT16_32_Q15(scale, yc.i), scale_shift);

-#else

-         yc.r *= st->scale;

-         yc.i *= st->scale;

+         yc.r = SHR32(yc.r, scale_shift);

+         yc.i = SHR32(yc.i, scale_shift);

 #endif

          f2[st->bitrev[i]] = yc;

       }