can: isotp: add symbolic error message to isotp_module_init()

This patch adds the value of err with format %pe to the already
existing error message.

Link: https://lore.kernel.org/r/20210427052150.2308-3-menschel.p@posteo.de
Signed-off-by: Patrick Menschel <menschel.p@posteo.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

net/can/isotp.c

@@ -1433,7 +1433,7 @@ static __init int isotp_module_init(void)
 
 	err = can_proto_register(&isotp_can_proto);
 	if (err < 0)
-		pr_err("can: registration of isotp protocol failed\n");
+		pr_err("can: registration of isotp protocol failed %pe\n", ERR_PTR(err));
 
 	return err;
 }