fix: Return default value from ‘GetCacheTypeString’

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 0 from that function. The
return value is then checked by an assert in the
AddMapEntry. The assert will only work in debug mode,
but that seems to be enough.

src/utils/list_cpu_features.c

@@ -340,6 +340,8 @@ static Node* GetCacheTypeString(CacheType cache_type) {
     case CPU_FEATURE_CACHE_PREFETCH:
       return CreateConstantString("prefetch");
   }
+  /* Should never happen */
+  return 0;
 }
 
 static void AddCacheInfo(Node* root, const CacheInfo* cache_info) {