Atomics: Make naming more obvious about which value is being returned

intern/cycles/util/util_stats.h

@@ -29,13 +29,13 @@ public:
 	explicit Stats(static_init_t) {}
 
 	void mem_alloc(size_t size) {
-		atomic_add_z(&mem_used, size);
+		atomic_add_and_fetch_z(&mem_used, size);
 		atomic_update_max_z(&mem_peak, mem_used);
 	}
 
 	void mem_free(size_t size) {
 		assert(mem_used >= size);
-		atomic_sub_z(&mem_used, size);
+		atomic_sub_and_fetch_z(&mem_used, size);
 	}
 
 	size_t mem_used;