fix CAN MAINTAINERS SCM tree type

As pointed out by Joe Perches the SCM tree type was missing in my patch.

Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

CC: Oliver Hartkopp <oliver.hartkopp@volkswagen.de>
CC: Urs Thuermann <urs.thuermann@volkswagen.de>
CC: Wolfgang Grandegger <wg@grandegger.com>
CC: Marc Kleine-Budde <mkl@pengutronix.de>
CC: linux-can@vger.kernel.org