[HTML5] Use browser mix rate by default on the Web.

Browsers doesn't really like forcing the mix rate, e.g. Firefox does not
allow input (microphone) if the mix rate is not the default one, Chrom*
will exhibit worse performances, etc.

platform/javascript/audio_driver_javascript.cpp

@@ -108,7 +108,7 @@ Error AudioDriverJavaScript::init() {
 	mix_rate = GLOBAL_GET("audio/driver/mix_rate");
 	int latency = GLOBAL_GET("audio/driver/output_latency");
 
-	channel_count = godot_audio_init(mix_rate, latency, &_state_change_callback, &_latency_update_callback);
+	channel_count = godot_audio_init(&mix_rate, latency, &_state_change_callback, &_latency_update_callback);
 	buffer_length = closest_power_of_2((latency * mix_rate / 1000));
 #ifndef NO_THREADS
 	node = memnew(WorkletNode);