layers: Fix incorrect generation of get_debug_report_enum
layers: Fix incorrect generation of get_debug_report_enum

There is no corresponding DebugReportObjectType enum for
kVulkanObjectTypeDebugUtilsMessengerEXT, so map it to the unknown type.

The generation script skipped over this enum, causing buffer overflow
faults in the VkLayerTest.ValidationCacheTestBadMerge test.

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