kmscube: update the project URL

kmscube repository has been moved to freedesktop.org, so
update the URL accordingly.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/kmscube/Config.in

@@ -6,4 +6,4 @@ config BR2_PACKAGE_KMSCUBE
 	help
 	  kmscube is an application to test kms/drm drivers.
 
-	  https://github.com/robclark/kmscube/
+	  https://cgit.freedesktop.org/mesa/kmscube/