layers: GH7, Fix bad var names in core_validation

Change-Id: I4fd1b8bb1cb83af633e04fc561771b6d76732588
diff --git a/layers/descriptor_sets.h b/layers/descriptor_sets.h
index 58e3b5c..bf8e29d 100644
--- a/layers/descriptor_sets.h
+++ b/layers/descriptor_sets.h
@@ -141,7 +141,7 @@
  */
 
 // Slightly broader than type, each c++ "class" will has a corresponding "DescriptorClass"
-typedef enum _DescriptorClass { PlainSampler, ImageSampler, Image, TexelBuffer, GeneralBuffer } DescriptorClass;
+enum DescriptorClass { PlainSampler, ImageSampler, Image, TexelBuffer, GeneralBuffer };
 
 class Descriptor {
   public: