virtio_ring: add a struct device forward declaration

The virtio_ring header file uses the struct device without a forward
declaration.
Signed-off-by: Shunsuke Mie <mie@igel.co.jp>
Message-Id: <20230417022037.917668-1-mie@igel.co.jp>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

include/linux/virtio_ring.h

@@ -58,6 +58,7 @@ do { \
 
 struct virtio_device;
 struct virtqueue;
+struct device;
 
 /*
  * Creates a virtqueue and allocates the descriptor ring.  If