rcu: Fix an obsolete ->qsmaskinit comment

Back in the old days, when grace-period initialization blocked CPU
hotplug, the ->qsmaskinit mask was indeed updated at the time that
a given CPU went offline.  However, with the deferral of these updates
until the beginning of the next grace period in commit 0aa04b055e
("rcu: Process offlining and onlining only at grace-period start"),
it is instead ->qsmaskinitnext that gets updated at that time.

This commit therefore updates the obsolete comment.  It also fixes
punctuation while on the topic of comments mentioning ->qsmaskinit.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcu/tree.c

@@ -2438,7 +2438,7 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
  * This function therefore goes up the tree of rcu_node structures,
  * clearing the corresponding bits in the ->qsmaskinit fields.  Note that
  * the leaf rcu_node structure's ->qsmaskinit field has already been
- * updated
+ * updated.
  *
  * This function does check that the specified rcu_node structure has
  * all CPUs offline and no blocked tasks, so it is OK to invoke it
@@ -3709,7 +3709,7 @@ void rcu_cpu_starting(unsigned int cpu)
 #ifdef CONFIG_HOTPLUG_CPU
 /*
  * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
- * function.  We now remove it from the rcu_node tree's ->qsmaskinit
+ * function.  We now remove it from the rcu_node tree's ->qsmaskinitnext
  * bit masks.
  */
 static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)