sched: don't clear PF_VCPU in scheduler

KVM clears it by itself now, and for s390 this is plain wrong.
Signed-off-by: Laurent Vivier <Laurent.Vivier@bull.net>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Avi Kivity <avi@qumranet.com>

kernel/sched.c

@@ -3375,7 +3375,6 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
 
 	if (p->flags & PF_VCPU) {
 		account_guest_time(p, cputime);
-		p->flags &= ~PF_VCPU;
 		return;
 	}