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/flexcan.c b/drivers/net/can/flexcan.c
index 1b6f562..c8a6fc7 100644
--- a/drivers/net/can/flexcan.c
+++ b/drivers/net/can/flexcan.c
@@ -203,7 +203,7 @@
 	.hw_ver = 10,
 };
 
-static struct can_bittiming_const flexcan_bittiming_const = {
+static const struct can_bittiming_const flexcan_bittiming_const = {
 	.name = DRV_NAME,
 	.tseg1_min = 4,
 	.tseg1_max = 16,