output: move functions into the AudioOutput struct

src/output/plugins/SolarisOutputPlugin.cxx

@@ -61,7 +61,7 @@ struct SolarisOutput {
 		:base(solaris_output_plugin) {}
 
 	bool Initialize(const config_param &param, Error &error_r) {
-		return ao_base_init(&base, param, error_r);
+		return base.Configure(param, error_r);
 	}
 };