Add missing module license tag to vring helpers.

[ 624.286653] vringh: module license 'unspecified' taints kernel.

Signed-off-by: Dave Jones <[e-mail]>
Signed-off-by: Rusty Russell <[e-mail]>

drivers/vhost/vringh.c

···
  *
  * Since these may be in userspace, we use (inline) accessors.
  */
+#include <linux/module.h>
 #include <linux/vringh.h>
 #include <linux/virtio_ring.h>
 #include <linux/kernel.h>
···
 	return __vringh_need_notify(vrh, getu16_kern);
 }
 EXPORT_SYMBOL(vringh_need_notify_kern);
+
+MODULE_LICENSE("GPL");