input: Add notify_touch_cancel()

We already have notify_touch(), notify_touch_frame().  We need
notify_touch_cancel() to implement touch in the weston wayland backend
properly.

Reviewed-by: Daniel Stone <daniels@collabora.com>
Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
diff --git a/src/input.c b/src/input.c
index 097c8e7..f5bb54e 100644
--- a/src/input.c
+++ b/src/input.c
@@ -1807,6 +1807,15 @@
 	grab->interface->frame(grab);
 }
 
+WL_EXPORT void
+notify_touch_cancel(struct weston_seat *seat)
+{
+	struct weston_touch *touch = weston_seat_get_touch(seat);
+	struct weston_touch_grab *grab = touch->grab;
+
+	grab->interface->cancel(grab);
+}
+
 static int
 pointer_cursor_surface_get_label(struct weston_surface *surface,
 				 char *buf, size_t len)