can: peak_usb: pcan_usb_{,pro}_get_device_id(): remove unneeded check for device_id

The callback struct peak_usb_adapter::dev_get_device_id, which is
implemented by the functions pcan_usb_{,pro}_get_device_id() is only
ever called with a valid device_id pointer.

This patch removes the unneeded check if the device_id pointer is
valid.

Link: https://lore.kernel.org/r/20210406111622.1874957-7-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>