[IA64] fix section mismatch in arch/ia64/kernel/acpi.c

This patch kills:

	WARNING: vmlinux.o(.text+0x1702): Section mismatch in
	reference from the function acpi_register_ioapic() to the
	function .devinit.text:iosapic_init()
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/kernel/acpi.c

@@ -966,7 +966,7 @@ acpi_map_iosapics (void)
 fs_initcall(acpi_map_iosapics);
 #endif				/* CONFIG_ACPI_NUMA */
 
-int acpi_register_ioapic(acpi_handle handle, u64 phys_addr, u32 gsi_base)
+int __ref acpi_register_ioapic(acpi_handle handle, u64 phys_addr, u32 gsi_base)
 {
 	int err;