can: peak_usb: fix checkpatch warnings

This patch cleans several checkpatch warnings in the peak_usb driver.

Link: https://lore.kernel.org/r/20210406111622.1874957-2-mkl@pengutronix.de
Acked-by: Stephane Grosjean <s.grosjean@peak-system.com>
Tested-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>