demos: fix gcc warning
demos: fix gcc warning

Change-Id: I9f4371334bf958bb01e89621008b6e569002d9a1

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