clients: Adjust grammar of comment for toysurface->prepare function pointer

Signed-off-by: Chris Michael <cp.michael@samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
diff --git a/clients/window.c b/clients/window.c
index bf3c470..5d69116 100644
--- a/clients/window.c
+++ b/clients/window.c
@@ -145,7 +145,7 @@
 
 struct toysurface {
 	/*
-	 * Prepare the surface for drawing. Makes sure there is a surface
+	 * Prepare the surface for drawing. Ensure there is a surface
 	 * of the right size available for rendering, and return it.
 	 * dx,dy are the x,y of wl_surface.attach.
 	 * width,height are the new buffer size.