demos: call DeviceWaitIdle before DestroyDevice
demos: call DeviceWaitIdle before DestroyDevice

Change-Id: Ic5819027b706e8c5d66ae78d0d0da1133c16085b

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools