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: Ingo Molnar <mingo@elte.hu>
  * 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 {