sched: fix sched_info_switch not being called according to documentation

http://bugzilla.kernel.org/show_bug.cgi?id=10545

sched_stats.h says that __sched_info_switch is "called when prev !=
next" in the comment.  sched.c should therefore do that.
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched.c

@@ -4662,9 +4662,9 @@ asmlinkage void __sched schedule(void)
 	prev->sched_class->put_prev_task(rq, prev);
 	next = pick_next_task(rq, prev);
 
-	sched_info_switch(prev, next);
-
 	if (likely(prev != next)) {
+		sched_info_switch(prev, next);
+
 		rq->nr_switches++;
 		rq->curr = next;
 		++*switch_count;