d3d9: Properly retrieve an interface pointer in d3d9_texture_cube_UnlockRect().

dlls/d3d9/texture.c

@@ -793,6 +793,7 @@ static HRESULT WINAPI d3d9_texture_cube_UnlockRect(IDirect3DCubeTexture9 *iface,
 {
     struct d3d9_texture *texture = impl_from_IDirect3DCubeTexture9(iface);
     struct wined3d_resource *sub_resource;
+    IDirect3DSurface9Impl *surface_impl;
     UINT sub_resource_idx;
     HRESULT hr;
 
@@ -803,7 +804,10 @@ static HRESULT WINAPI d3d9_texture_cube_UnlockRect(IDirect3DCubeTexture9 *iface,
     if (!(sub_resource = wined3d_texture_get_sub_resource(texture->wined3d_texture, sub_resource_idx)))
         hr = D3DERR_INVALIDCALL;
     else
-        hr = IDirect3DSurface9_UnlockRect((IDirect3DSurface9 *)wined3d_resource_get_parent(sub_resource));
+    {
+        surface_impl = wined3d_resource_get_parent(sub_resource);
+        hr = IDirect3DSurface9_UnlockRect(&surface_impl->IDirect3DSurface9_iface);
+    }
     wined3d_mutex_unlock();
 
     return hr;