x86/hpet: Use proper hpet device number for MSI allocation

hpet_assign_irq() is called with hpet_device->num as "hardware
interrupt number", but hpet_device->num is initialized after the
interrupt has been assigned, so it's always 0. As a consequence only
the first MSI allocation succeeds, the following ones fail because the
"hardware interrupt number" already exists.

Move the initialization of dev->num and other fields before the call
to hpet_assign_irq(), which is the ordering before the offending
commit which introduced that regression.

Fixes: "3cb96f0c9733 x86/hpet: Enhance HPET IRQ to support hierarchical irqdomains"
Reported-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/alpine.DEB.2.11.1506211635010.4107@nanos
Cc: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>

arch/x86/kernel/hpet.c

@@ -577,16 +577,17 @@ static void hpet_msi_capability_lookup(unsigned int start_timer)
 		if (!(cfg & HPET_TN_FSB_CAP))
 			continue;
 
+		hdev->flags = 0;
+		if (cfg & HPET_TN_PERIODIC_CAP)
+			hdev->flags |= HPET_DEV_PERI_CAP;
+		sprintf(hdev->name, "hpet%d", i);
+		hdev->num = i;
+
 		irq = hpet_assign_irq(hpet_domain, hdev, hdev->num);
 		if (irq <= 0)
 			continue;
 
-		sprintf(hdev->name, "hpet%d", i);
-		hdev->num = i;
 		hdev->irq = irq;
-		hdev->flags = 0;
-		if (cfg & HPET_TN_PERIODIC_CAP)
-			hdev->flags |= HPET_DEV_PERI_CAP;
 		hdev->flags |= HPET_DEV_FSB_CAP;
 		hdev->flags |= HPET_DEV_VALID;
 		num_timers_used++;