wasapi: fix memory leak

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
(cherry picked from commit 6db8aefc4e1c8fd8397e76c4b222aec63ee15ba2)

modules/audio_output/wasapi.c

@@ -450,6 +450,8 @@ static void Stop(aout_stream_t *s)
 
     IAudioClient_Stop(sys->client); /* should not be needed */
     IAudioClient_Release(sys->client);
+
+    free(sys);
 }
 
 vlc_module_begin()