drivers: can: increase default initialization priority from 50 to 80

Increase the default CAN controller driver initialization priority from
KERNEL_INIT_PRIORITY_DEVICE (50) to 80 to allow CAN controllers on SPI
busses have their bus initialized prior to initializing the CAN controller
driver.

The only in-bound dependency on CAN controller drivers - apart from
application level code - is the drivers/net/canbus.c driver, which already
defaults to an initialization level of 81.

Fixes: #55745

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>