drm/virtio: fix up for include file changes

virtgpu_kms now uses VIRTIO_RING_F_INDIRECT_DESC, so it must
include virtio_ring.h directly.

Fixes: 5edbb56 ("drm/virtio: fix ring free check")
Signed-off-by: Stephen Rothwell <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Michael S. Tsirkin <[email protected]>

Author: sfrothwell

drivers/gpu/drm/virtio/virtgpu_kms.c

@@ -25,6 +25,7 @@
 
 #include <linux/virtio.h>
 #include <linux/virtio_config.h>
+#include <linux/virtio_ring.h>
 
 #include <drm/drm_file.h>