sched/topology: Improve comments

Mike provided a better comment for destroy_sched_domain() ...
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: NIngo Molnar <mingo@kernel.org>

kernel/sched/topology.c

@@ -344,8 +344,9 @@ static void free_sched_groups(struct sched_group *sg, int free_sgc)
 static void destroy_sched_domain(struct sched_domain *sd)
 {
 	/*
-	 * A sched domain has many groups' reference, and an overlapping
-	 * domain has private groups, iterate and nuke them all.
+	 * A normal sched domain may have multiple group references, an
+	 * overlapping domain, having private groups, only one.  Iterate,
+	 * dropping group/capacity references, freeing where none remain.
 	 */
 	free_sched_groups(sd->groups, 1);