tcm_vhost: Use llist for cmd completion list

This drops the cmd completion list spin lock and makes the cmd
completion queue lock-less.

Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/vhost/tcm_vhost.h b/drivers/vhost/tcm_vhost.h
index 7e87c63..47ee80b 100644
--- a/drivers/vhost/tcm_vhost.h
+++ b/drivers/vhost/tcm_vhost.h
@@ -34,7 +34,7 @@
 	/* Sense buffer that will be mapped into outgoing status */
 	unsigned char tvc_sense_buf[TRANSPORT_SENSE_BUFFER];
 	/* Completed commands list, serviced from vhost worker thread */
-	struct list_head tvc_completion_list;
+	struct llist_node tvc_completion_list;
 };
 
 struct tcm_vhost_nexus {