Unified multiple definitions of container_of() macro.

Removed duplicate definitions of the container_of() macro and
refactored sources to use the single implementation.

Signed-off-by: Jon A. Cruz <jonc@osg.samsung.com>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
diff --git a/clients/clickdot.c b/clients/clickdot.c
index b522974..776f8da 100644
--- a/clients/clickdot.c
+++ b/clients/clickdot.c
@@ -40,6 +40,7 @@
 #include <wayland-client.h>
 
 #include "window.h"
+#include "shared/helpers.h"
 
 struct clickdot {
 	struct display *display;