clocksource/drivers/c-sky: fixup qemu fail to bootup sometimes.

Timer startup must after timer_irq_enable. For qemu, timer tick
irq hanppens but irq not enable, so it will cause qemu boot failed.
Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Tested-by: Liu Zhiwei <zhiwei_liu@c-sky.com>

drivers/clocksource/timer-mp-csky.c

@@ -79,11 +79,11 @@ static int csky_mptimer_starting_cpu(unsigned int cpu)
 
 	to->clkevt.cpumask = cpumask_of(cpu);
 
+	enable_percpu_irq(csky_mptimer_irq, 0);
+
 	clockevents_config_and_register(&to->clkevt, timer_of_rate(to),
 					2, ULONG_MAX);
 
-	enable_percpu_irq(csky_mptimer_irq, 0);
-
 	return 0;
 }