external: Back up one spirv-tools commit
external: Back up one spirv-tools commit

As a workaround for the assert running CTS with validation, back
up one spirv-tools commit until SPIRV-Tools issue 517 is resolved

Change-Id: I4b173add841a67654caabd4fd534fe00a8970009

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