ia64/xen: fix the link error.

This patch fixes the following link error with xen_domu_defconfig.
Depending on compiler version, it doesn't link as follows.
So remove const and use __initdata for xen_iosapic_ops.

> arch/ia64/xen/xen_pv_ops.c:878: error: xen_iosapic_ops causes a section type conflict
Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
Signed-off-by: Tony Luck <tony.luck@intel.com>

arch/ia64/xen/xen_pv_ops.c

@@ -875,7 +875,7 @@ xen_iosapic_write(char __iomem *iosapic, unsigned int reg, u32 val)
 	HYPERVISOR_physdev_op(PHYSDEVOP_apic_write, &apic_op);
 }
 
-static const struct pv_iosapic_ops xen_iosapic_ops __initconst = {
+static struct pv_iosapic_ops xen_iosapic_ops __initdata = {
 	.pcat_compat_init = xen_pcat_compat_init,
 	.__get_irq_chip = xen_iosapic_get_irq_chip,