can: raw: raw_bind(): bail out if can_family is not AF_CAN

Until now CAN raw's bind() doesn't check if the can_familiy in the
struct sockaddr_can is set to AF_CAN. This patch adds the missing check.

Acked-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>