can: mark bittiming_const pointer in struct can_priv as const

This patch marks the bittiming_const pointer as in the struct can_pric as
"const". This allows us to mark the struct can_bittiming_const in the CAN
drivers as "const", too.

Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
diff --git a/drivers/net/can/bfin_can.c b/drivers/net/can/bfin_can.c
index ea31438..f2d6d25 100644
--- a/drivers/net/can/bfin_can.c
+++ b/drivers/net/can/bfin_can.c
@@ -44,7 +44,7 @@
 /*
  * bfin can timing parameters
  */
-static struct can_bittiming_const bfin_can_bittiming_const = {
+static const struct can_bittiming_const bfin_can_bittiming_const = {
 	.name = DRV_NAME,
 	.tseg1_min = 1,
 	.tseg1_max = 16,