ARM: dts: stm32f429: put can2 in secondary mode

This is a preparation patch for the upcoming support to manage CAN
peripherals in single configuration.

The addition ensures backwards compatibility.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Link: https://lore.kernel.org/all/20230427204540.3126234-3-dario.binacchi@amarulasolutions.com


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>