sink, source: Prevent unnecessary rate update attempts

We don't need to try a rate update if the desired sample rate is the
same as the one the sink or source is already using.

src/pulsecore/sink.c

@@ -1392,6 +1392,9 @@ pa_bool_t pa_sink_update_rate(pa_sink *s, uint32_t rate, pa_bool_t passthrough)
             desired_rate = rate; /* use stream sampling rate, discard default/alternate settings */
         }
 
+        if (desired_rate == s->sample_spec.rate)
+            return FALSE;
+
         if (!passthrough && pa_sink_used_by(s) > 0)
             return FALSE;