[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>