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/src/libinput-device.c b/src/libinput-device.c
index 9fba25e..2cbfb88 100644
--- a/src/libinput-device.c
+++ b/src/libinput-device.c
@@ -38,6 +38,7 @@
 
 #include "compositor.h"
 #include "libinput-device.h"
+#include "shared/helpers.h"
 
 #define DEFAULT_AXIS_STEP_DISTANCE wl_fixed_from_int(10)