can: peak_usb: pcan_usb_get_serial(): make use of le32_to_cpup()

This patch replaces the memcpy() + le32_to_cpu() by le32_to_cpup().

Link: https://lore.kernel.org/r/20210406111622.1874957-9-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>