dmusic: Remove superfluous casts to self.

dlls/dmusic/dmobject.c

@@ -466,7 +466,7 @@ HRESULT stream_get_object(IStream *stream, DMUS_OBJECTDESC *desc, REFIID iid, vo
 
     if (SUCCEEDED(hr = stream_get_loader(stream, &loader)))
     {
-        hr = IDirectMusicLoader_GetObject(loader, desc, iid, (void **)ret_iface);
+        hr = IDirectMusicLoader_GetObject(loader, desc, iid, ret_iface);
         IDirectMusicLoader_Release(loader);
     }
 

dlls/dmusic/tests/dmusic.c

@@ -1078,7 +1078,7 @@ static void test_port_download(void)
     ok(hr == S_OK, "got %#lx\n", hr);
     size = 0xdeadbeef;
     buffer = invalid_ptr;
-    hr = IDirectMusicDownload_GetBuffer(download, (void **)&buffer, &size);
+    hr = IDirectMusicDownload_GetBuffer(download, &buffer, &size);
     ok(hr == S_OK, "got %#lx\n", hr);
     ok(size == 1, "got %#lx\n", size);
     ok(buffer != invalid_ptr, "got %p\n", buffer);