examples/accel_perf: correct the unlock operation

Change-Id: I43e54ceae1184483747dff70d224a7aa2b24a6fd
Signed-off-by: GangCao <gang.cao@intel.com>
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/16006
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Shuhei Matsumoto <smatsumoto@nvidia.com>
Reviewed-by: Aleksey Marchuk <alexeymar@nvidia.com>
Community-CI: Mellanox Build Bot

examples/accel/perf/accel_perf.c

@@ -265,8 +265,9 @@ unregister_worker(void *arg1)
 		pthread_mutex_unlock(&g_workers_lock);
 		g_rc = dump_result();
 		spdk_app_stop(0);
-	}
+	} else {
 		pthread_mutex_unlock(&g_workers_lock);
+	}
 }
 
 static void