can: peak_usb: use ARRAY_SIZE instead of NULL termination for peak_usb_adapters_list

This patch converts the list "static struct peak_usb_adapter
*peak_usb_adapters_list[]" to be used with ARRAY_SIZE not with a NULL
termination, as the size is known during compile time.

Acked-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>