can: peak_usb: pcan_dump_mem(): mark input prompt and data pointer as const

Mark the input prompt and data pointer as const.

Link: https://lore.kernel.org/all/20220719120632.26774-1-s.grosjean@peak-system.com


Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
[mkl: mark data pointer as const, too; update commit message]
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>