Fix warning - extra ';' for -Wextra-semi (#3198)

Signed-off-by: hydai <z54981220@gmail.com>

bench/async_bench.cpp

@@ -146,7 +146,7 @@ void bench_mt(int howmany, std::shared_ptr<spdlog::logger> logger, int thread_co
 
     for (auto &t : threads) {
         t.join();
-    };
+    }
 
     auto delta = high_resolution_clock::now() - start;
     auto delta_d = duration_cast<duration<double>>(delta).count();