ACPI: silence ia64 build warning

When building sim_defconfig, which does not define CONFIG_ACPI
arch/ia64/kernel/acpi.c:71: warning: 'acpi_madt_rev' defined but not used

really acpi.c should not be built when CONFIG_ACPI=n...
Signed-off-by: Len Brown <len.brown@intel.com>

arch/ia64/kernel/acpi.c

@@ -68,8 +68,6 @@ EXPORT_SYMBOL(pm_power_off);
 unsigned char acpi_kbd_controller_present = 1;
 unsigned char acpi_legacy_devices;
 
-static unsigned int __initdata acpi_madt_rev;
-
 unsigned int acpi_cpei_override;
 unsigned int acpi_cpei_phys_cpuid;
 
@@ -243,6 +241,8 @@ acpi_parse_iosapic(acpi_table_entry_header * header, const unsigned long end)
 	return iosapic_init(iosapic->address, iosapic->global_irq_base);
 }
 
+static unsigned int __initdata acpi_madt_rev;
+
 static int __init
 acpi_parse_plat_int_src(acpi_table_entry_header * header,
 			const unsigned long end)