virtio-mmio: Use to_virtio_mmio_device() to simply code

The file virtio_mmio.c has defined the function to_virtio_mmio_device,
so use it instead of container_of() to simply code.
Signed-off-by: Tang Bin <tangbin@cmss.chinamobile.com>
Link: https://lore.kernel.org/r/20210222055724.220-1-tangbin@cmss.chinamobile.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>

drivers/virtio/virtio_mmio.c

@@ -548,8 +548,7 @@ static void virtio_mmio_release_dev(struct device *_d)
 {
 	struct virtio_device *vdev =
 			container_of(_d, struct virtio_device, dev);
-	struct virtio_mmio_device *vm_dev =
-			container_of(vdev, struct virtio_mmio_device, vdev);
+	struct virtio_mmio_device *vm_dev = to_virtio_mmio_device(vdev);
 	struct platform_device *pdev = vm_dev->pdev;
 
 	devm_kfree(&pdev->dev, vm_dev);