sched: Fix proc_sched_set_task()

Latencytop clearing sum_exec_runtime via proc_sched_set_task() breaks
task_times().  Other places in kernel use nvcsw and nivcsw, which are
being cleared as well,  Clear task statistics only.
Reported-by: Török Edwin <edwintorok@gmail.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Cc: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1269940193.19286.14.camel@marge.simson.net>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/sched_debug.c

@@ -518,8 +518,4 @@ void proc_sched_set_task(struct task_struct *p)
 	p->se.nr_wakeups_idle			= 0;
 	p->sched_info.bkl_count			= 0;
 #endif
-	p->se.sum_exec_runtime			= 0;
-	p->se.prev_sum_exec_runtime		= 0;
-	p->nvcsw				= 0;
-	p->nivcsw				= 0;
 }