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>

drivers/net/can/usb/peak_usb/pcan_usb_core.h

@@ -45,7 +45,7 @@ struct peak_usb_adapter {
 	char *name;
 	u32 device_id;
 	struct can_clock clock;
-	struct can_bittiming_const bittiming_const;
+	const struct can_bittiming_const bittiming_const;
 	unsigned int ctrl_count;
 
 	int (*intf_probe)(struct usb_interface *intf);