shell: Make panel just a wl_surface too
diff --git a/protocol/desktop-shell.xml b/protocol/desktop-shell.xml
index 97b6b4f..1edd011 100644
--- a/protocol/desktop-shell.xml
+++ b/protocol/desktop-shell.xml
@@ -14,7 +14,7 @@
 
     <request name="set_panel">
       <arg name="output" type="object" interface="wl_output"/>
-      <arg name="surface" type="object" interface="wl_shell_surface"/>
+      <arg name="surface" type="object" interface="wl_surface"/>
     </request>
 
     <request name="set_lock_surface">