x86: fix unused variable warning in arch/x86/kernel/hpet.c

Impact: fix build warning

this warning:

  arch/x86/kernel/hpet.c:36: warning: ‘hpet_num_timers’ defined but not used

Triggers because hpet_num_timers is unused in the !CONFIG_PCI_MSI case.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/hpet.c

@@ -33,7 +33,9 @@
  * HPET address is set in acpi/boot.c, when an ACPI entry exists
  */
 unsigned long				hpet_address;
+#ifdef CONFIG_PCI_MSI
 static unsigned long			hpet_num_timers;
+#endif
 static void __iomem			*hpet_virt_address;
 
 struct hpet_dev {