scripts: Make object string conversion array const
scripts: Make object string conversion array const

Prevents unused var warnings by changing to be a constant.

Change-Id: Ie8f6cc837dd589074ae2278de34d4bd0a3e66236

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