avfilter/af_mcompand: compute half frequency in double

Fixes: CID1422217 Result is not floating-point

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit 2d0d502ff1)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/af_mcompand.c

@@ -417,8 +417,8 @@ static int config_output(AVFilterLink *outlink)
         }
 
         new_nb_items += sscanf(tstr2, "%lf", &s->bands[i].topfreq) == 1;
-        if (s->bands[i].topfreq < 0 || s->bands[i].topfreq >= outlink->sample_rate / 2) {
-            av_log(ctx, AV_LOG_ERROR, "crossover_frequency: %f, should be >=0 and lower than half of sample rate: %d.\n", s->bands[i].topfreq, outlink->sample_rate / 2);
+        if (s->bands[i].topfreq < 0 || s->bands[i].topfreq >= outlink->sample_rate / 2.0) {
+            av_log(ctx, AV_LOG_ERROR, "crossover_frequency: %f, should be >=0 and lower than half of sample rate: %f.\n", s->bands[i].topfreq, outlink->sample_rate / 2.0);
             return AVERROR(EINVAL);
         }