wasapi: Fixed some compiler warnings.

src/audio/wasapi/SDL_wasapi_win32.c

@@ -188,7 +188,6 @@ SDLMMNotificationClient_OnDeviceRemoved(IMMNotificationClient *ithis, LPCWSTR pw
 static HRESULT STDMETHODCALLTYPE
 SDLMMNotificationClient_OnDeviceStateChanged(IMMNotificationClient *ithis, LPCWSTR pwstrDeviceId, DWORD dwNewState)
 {
-    SDLMMNotificationClient *this = (SDLMMNotificationClient *) ithis;
     IMMDevice *device = NULL;
 
     if (SUCCEEDED(IMMDeviceEnumerator_GetDevice(enumerator, pwstrDeviceId, &device))) {
@@ -232,7 +231,7 @@ static const IMMNotificationClientVtbl notification_client_vtbl = {
     SDLMMNotificationClient_OnPropertyValueChanged
 };
 
-static SDLMMNotificationClient notification_client = { &notification_client_vtbl, 1 };
+static SDLMMNotificationClient notification_client = { &notification_client_vtbl, { 1 } };
 
 
 int