x86/xen/time: fix section mismatch for xen_init_time_ops()

The header declares this function as __init but is defined in __ref
section.
Signed-off-by: Nick Desaulniers <nick.desaulniers@gmail.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

arch/x86/xen/xen-ops.h

@@ -71,7 +71,7 @@ u64 xen_clocksource_read(void);
 void xen_setup_cpu_clockevents(void);
 void xen_save_time_memory_area(void);
 void xen_restore_time_memory_area(void);
-void __init xen_init_time_ops(void);
+void __ref xen_init_time_ops(void);
 void __init xen_hvm_init_time_ops(void);
 
 irqreturn_t xen_debug_interrupt(int irq, void *dev_id);