cpus: initialize timers_state.vm_clock_lock

We forgot to initialize the spinlock introduced in 94377115
("cpus: protect TimerState writes with a spinlock", 2018-08-23).
Fix it.
Signed-off-by: NEmilio G. Cota <cota@braap.org>
Message-Id: <20180903171831.15446-5-cota@braap.org>
Reviewed-by: NAlex Bennée <alex.bennee@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

cpus.c

@@ -823,6 +823,7 @@ int cpu_throttle_get_percentage(void)
 void cpu_ticks_init(void)
 {
     seqlock_init(&timers_state.vm_clock_seqlock);
+    qemu_spin_init(&timers_state.vm_clock_lock);
     vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
     throttle_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL_RT,
                                            cpu_throttle_timer_tick, NULL);