eac3dec: fix scaling

This is the remaining error, the output on the SPX samples,
respectively csi_miami_stereo_128_spx.eac3 and
csi_miami_5.1_256_spx.eac3, goes from:
stddev:    8.71 PSNR: 77.52 MAXDIFF:  235
stddev:24270.51 PSNR: 22.17 MAXDIFF:47166
to:
stddev:    0.12 PSNR:114.12 MAXDIFF:    1
stddev:    0.12 PSNR:114.73 MAXDIFF:    1

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 0c3339f4bd)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/eac3dec.c

@@ -143,7 +143,9 @@ static void ff_eac3_apply_spectral_extension(AC3DecodeContext *s)
             float nscale = s->spx_noise_blend[ch][bnd] * rms_energy[bnd] * (1.0f / INT32_MIN);
             float sscale = s->spx_signal_blend[ch][bnd];
 #if USE_FIXED
+            // spx_noise_blend and spx_signal_blend are both FP.23
             nscale *= 1.0 / (1<<23);
+            sscale *= 1.0 / (1<<23);
 #endif
             for (i = 0; i < s->spx_band_sizes[bnd]; i++) {
                 float noise  = nscale * (int32_t)av_lfg_get(&s->dith_state);