x86/Xen: mark xen_setup_gdt() __init

Its only caller is __init, so to avoid section mismatch warnings when a
compiler decides to not inline the function marke this function so as
well. Take the opportunity and also make the function actually use its
argument: The sole caller passes in zero anyway.
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/x86/xen/enlighten_pv.c

@@ -1170,13 +1170,13 @@ static void __init xen_boot_params_init_edd(void)
  * we do this, we have to be careful not to call any stack-protected
  * function, which is most of the kernel.
  */
-static void xen_setup_gdt(int cpu)
+static void __init xen_setup_gdt(int cpu)
 {
 	pv_cpu_ops.write_gdt_entry = xen_write_gdt_entry_boot;
 	pv_cpu_ops.load_gdt = xen_load_gdt_boot;
 
-	setup_stack_canary_segment(0);
-	switch_to_new_gdt(0);
+	setup_stack_canary_segment(cpu);
+	switch_to_new_gdt(cpu);
 
 	pv_cpu_ops.write_gdt_entry = xen_write_gdt_entry;
 	pv_cpu_ops.load_gdt = xen_load_gdt;