fix: Return default value from ‘GetCacheTypeString’ (#162)

The build fails with following message when -Werror
and -Werror=return-type are enabled.

In function ‘GetCacheTypeString’:
	error: control reaches end of non-void function [-Werror=return-type]

Simple fix is to return explicitly communicate to
the compiler that certain block is not reachable.

src/utils/list_cpu_features.c

@@ -340,6 +340,7 @@ static Node* GetCacheTypeString(CacheType cache_type) {
     case CPU_FEATURE_CACHE_PREFETCH:
       return CreateConstantString("prefetch");
   }
+  UNREACHABLE();
 }
 
 static void AddCacheInfo(Node* root, const CacheInfo* cache_info) {