d3d9: Finish the COM cleanup of the IDirect3DDevice9Ex iface.
diff --git a/dlls/d3d9/buffer.c b/dlls/d3d9/buffer.c
index 827a191..f10e531 100644
--- a/dlls/d3d9/buffer.c
+++ b/dlls/d3d9/buffer.c
@@ -281,7 +281,7 @@
         return hr;
     }
 
-    buffer->parentDevice = (IDirect3DDevice9Ex *)device;
+    buffer->parentDevice = &device->IDirect3DDevice9Ex_iface;
     IDirect3DDevice9Ex_AddRef(buffer->parentDevice);
 
     return D3D_OK;
@@ -544,7 +544,7 @@
         return hr;
     }
 
-    buffer->parentDevice = (IDirect3DDevice9Ex *)device;
+    buffer->parentDevice = &device->IDirect3DDevice9Ex_iface;
     IDirect3DDevice9Ex_AddRef(buffer->parentDevice);
 
     return D3D_OK;