cpus: hvf: unregister thread with RCU

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

cpus.c

@@ -1541,6 +1541,7 @@ static void *qemu_hvf_cpu_thread_fn(void *arg)
     cpu->created = false;
     qemu_cond_signal(&qemu_cpu_cond);
     qemu_mutex_unlock_iothread();
+    rcu_unregister_thread();
     return NULL;
 }