Documentation for the prepare_lock_surface event description, is incorrect

Documentation for the prepare_lock_surface event description is
incorrect. The summary says "Tell the client..." however the full-text
description says "tell the shell..."

Signed-off-by: Chris Michael <cp.michael@samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
Acked-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>

[This time include the actual changes.]

protocol/desktop-shell.xml

@@ -44,9 +44,9 @@
 
     <event name="prepare_lock_surface">
       <description summary="tell the client to create, set the lock surface">
-	Tell the shell we want it to create and set the lock surface, which is
+	Tell the client we want it to create and set the lock surface, which is
 	a GUI asking the user to unlock the screen. The lock surface is
-	announced with 'set_lock_surface'. Whether or not the shell actually
+	announced with 'set_lock_surface'. Whether or not the client actually
 	implements locking, it MUST send 'unlock' request to let the normal
         desktop resume.
       </description>