sgi-xpc: Replace deprecated CPU-hotplug functions.

The functions get_online_cpus() and put_online_cpus() have been
deprecated during the CPU hotplug rework. They map directly to
cpus_read_lock() and cpus_read_unlock().

Replace deprecated CPU-hotplug functions with the official version.
The behavior remains unchanged.

Cc: Robin Holt <[e-mail]>
Cc: Steve Wahl <[e-mail]>
Cc: Mike Travis <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Signed-off-by: Sebastian Andrzej Siewior <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/sgi-xp/xpc_uv.c

···
 {
 	int cpu;
 
-	get_online_cpus();
+	cpus_read_lock();
 
 	for_each_cpu(cpu, cpumask_of_node(nid)) {
 		xpc_activate_mq_uv =
···
 			break;
 	}
 	if (IS_ERR(xpc_activate_mq_uv)) {
-		put_online_cpus();
+		cpus_read_unlock();
 		return PTR_ERR(xpc_activate_mq_uv);
 	}
 
···
 	}
 	if (IS_ERR(xpc_notify_mq_uv)) {
 		xpc_destroy_gru_mq_uv(xpc_activate_mq_uv);
-		put_online_cpus();
+		cpus_read_unlock();
 		return PTR_ERR(xpc_notify_mq_uv);
 	}
 
-	put_online_cpus();
+	cpus_read_unlock();
 	return 0;
 }