demos: fix cube cmake
demos: fix cube cmake

Change-Id: Ia7a79bee7353ac484e691916591c585643a8753d

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers