x86/mmiotrace: 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.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20210803141621.780504-7-bigeasy@linutronix.de

arch/x86/mm/mmio-mod.c

@@ -376,12 +376,12 @@ static void enter_uniprocessor(void)
 		goto out;
 	}
 
-	get_online_cpus();
+	cpus_read_lock();
 	cpumask_copy(downed_cpus, cpu_online_mask);
 	cpumask_clear_cpu(cpumask_first(cpu_online_mask), downed_cpus);
 	if (num_online_cpus() > 1)
 		pr_notice("Disabling non-boot CPUs...\n");
-	put_online_cpus();
+	cpus_read_unlock();
 
 	for_each_cpu(cpu, downed_cpus) {
 		err = remove_cpu(cpu);