cpu/hotplug: Get rid of CPU_STARTING reference

CPU_STARTING is scheduled for removal. There is no use of it in drivers
and core code uses it only for compatibility with old-style CPU-hotplug
notifiers.  This patch removes therefore removes CPU_STARTING from an
RCU-related comment.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/cpu.c

@@ -889,7 +889,7 @@ void notify_cpu_starting(unsigned int cpu)
 	struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
 	enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
 
-	rcu_cpu_starting(cpu);  /* All CPU_STARTING notifiers can use RCU. */
+	rcu_cpu_starting(cpu);	/* Enables RCU usage on this CPU. */
 	while (st->state < target) {
 		struct cpuhp_step *step;