shell: Make the lock surface just a plain wl_surface too
diff --git a/protocol/desktop-shell.xml b/protocol/desktop-shell.xml
index 1edd011..65c97ef 100644
--- a/protocol/desktop-shell.xml
+++ b/protocol/desktop-shell.xml
@@ -18,7 +18,7 @@
     </request>
 
     <request name="set_lock_surface">
-      <arg name="surface" type="object" interface="wl_shell_surface"/>
+      <arg name="surface" type="object" interface="wl_surface"/>
     </request>
 
     <request name="unlock"/>