Fixed a compiler warning on Visual Studio.

src/audio/SDL_audio.c

@@ -972,7 +972,7 @@ open_audio_device(const char *devname, int iscapture,
     SDL_AudioDevice *device;
     SDL_bool build_cvt;
     void *handle = NULL;
-    int stream_len;
+    Uint32 stream_len;
     int i = 0;
 
     if (!SDL_WasInit(SDL_INIT_AUDIO)) {

src/audio/winmm/SDL_winmm.c

@@ -57,7 +57,7 @@ DETECT_DEV_IMPL(SDL_FALSE, Out, WAVEOUTCAPS)
 DETECT_DEV_IMPL(SDL_TRUE, In, WAVEINCAPS)
 
 static void
-WINMM_DetectDevices()
+WINMM_DetectDevices(void)
 {
     DetectWaveInDevs();
     DetectWaveOutDevs();