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/usb/esd_usb2.c b/drivers/net/can/usb/esd_usb2.c
index 09b1da5..bd36e55 100644
--- a/drivers/net/can/usb/esd_usb2.c
+++ b/drivers/net/can/usb/esd_usb2.c
@@ -871,7 +871,7 @@
 	.ndo_start_xmit = esd_usb2_start_xmit,
 };
 
-static struct can_bittiming_const esd_usb2_bittiming_const = {
+static const struct can_bittiming_const esd_usb2_bittiming_const = {
 	.name = "esd_usb2",
 	.tseg1_min = ESD_USB2_TSEG1_MIN,
 	.tseg1_max = ESD_USB2_TSEG1_MAX,