KVM: i8254: simplify atomics in kvm_pit_ack_irq

We already have a helper that does the same thing.
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/i8254.c

@@ -236,19 +236,9 @@ static void kvm_pit_ack_irq(struct kvm_irq_ack_notifier *kian)
 {
 	struct kvm_kpit_state *ps = container_of(kian, struct kvm_kpit_state,
 						 irq_ack_notifier);
-	int value;
 
 	spin_lock(&ps->inject_lock);
-	value = atomic_dec_return(&ps->pending);
-	if (value < 0)
-		/* spurious acks can be generated if, for example, the
-		 * PIC is being reset.  Handle it gracefully here
-		 */
-		atomic_inc(&ps->pending);
-	else if (value > 0 && ps->reinject)
-		/* in this case, we had multiple outstanding pit interrupts
-		 * that we needed to inject.  Reinject
-		 */
+	if (atomic_dec_if_positive(&ps->pending) > 0 && ps->reinject)
 		queue_kthread_work(&ps->pit->worker, &ps->pit->expired);
 	ps->irq_ack = 1;
 	spin_unlock(&ps->inject_lock);