can: slcan: slcan_init() convert printk(LEVEL ...) to pr_level()

Convert the last printk(LEVEL ...) to pr_level().

Link: https://lore.kernel.org/all/20220704125954.1587880-3-mkl@pengutronix.de


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>