virtio_input: Improve freeze handling

When executing suspend to ram, if lacking the operations
to reset device and free unused buffers before deleting
a vq, resource leaks and inconsistent device status will
appear.

According to chapter "3.3.1 Driver Requirements: Device Cleanup:"
of virtio-specification:
Driver MUST ensure a virtqueue isn’t live
(by device reset) before removing exposed
buffers.

Therefore, modify the virtinput_freeze function to reset the
device and delete the unused buffers before deleting the
virtqueue, just like virtinput_remove does.

Co-developed-by: Ying Xu <[e-mail]>
Signed-off-by: Ying Xu <[e-mail]>
Co-developed-by: Junnan Wu <[e-mail]>
Signed-off-by: Junnan Wu <[e-mail]>
Signed-off-by: Ying Gao <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Michael S. Tsirkin <[e-mail]>

drivers/virtio/virtio_input.c

···
 {
 	struct virtio_input *vi = vdev->priv;
 	unsigned long flags;
+	void *buf;
 
 	spin_lock_irqsave(&vi->lock, flags);
 	vi->ready = false;
 	spin_unlock_irqrestore(&vi->lock, flags);
 
+	virtio_reset_device(vdev);
+	while ((buf = virtqueue_detach_unused_buf(vi->sts)) != NULL)
+		kfree(buf);
 	vdev->config->del_vqs(vdev);
 	return 0;
 }