x86: assign IRQs to HPET timers, fix

Looks like IRQ 31 is assigned to timer 3, even without the patch!
I wonder who wrote the number 31. But the manual says that it is
zero by default.

I think we should check whether the timer has been allocated an IRQ before
proceeding to assign one to it.  Here is a patch that does this.

Signed-off-by: Balaji Rao <balajirrao@gmail.com>
Tested-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

drivers/char/hpet.c

@@ -852,6 +852,12 @@ int hpet_alloc(struct hpet_data *hdp)
 
 		timer = &hpet->hpet_timers[devp - hpetp->hp_dev];
 
+		/* Check if there's already an IRQ assigned to the timer */
+		if (hdp->hd_irq[i]) {
+			hpetp->hp_dev[i].hd_hdwirq = hdp->hd_irq[i];
+			continue;
+		}
+
 		hpet_config = readq(&timer->hpet_config);
 		irq_bitmap = (hpet_config & Tn_INT_ROUTE_CAP_MASK)
 			>> Tn_INT_ROUTE_CAP_SHIFT;