KVM: s390: virtio_ccw: reset errors for new I/O.

ccw_io_helper neglected to reset vcdev->err after a new channel
program had been successfully started, resulting in stale errors
delivered after one I/O failed. Reset the error after a new
channel program has been successfully started with no old I/O
pending.
Signed-off-by: NCornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: NGleb Natapov <gleb@redhat.com>

drivers/s390/kvm/virtio_ccw.c

@@ -133,8 +133,11 @@ static int ccw_io_helper(struct virtio_ccw_device *vcdev,
 	do {
 		spin_lock_irqsave(get_ccwdev_lock(vcdev->cdev), flags);
 		ret = ccw_device_start(vcdev->cdev, ccw, intparm, 0, 0);
-		if (!ret)
+		if (!ret) {
+			if (!vcdev->curr_io)
+				vcdev->err = 0;
 			vcdev->curr_io |= flag;
+		}
 		spin_unlock_irqrestore(get_ccwdev_lock(vcdev->cdev), flags);
 		cpu_relax();
 	} while (ret == -EBUSY);