dt-bindings: can: renesas,rcar-canfd: Make interrupt-names required

The Renesas R-Car CAN FD Controller always uses two or more interrupts.
Make the interrupt-names properties a required property, to make it
easier to identify the individual interrupts.

Update the example accordingly.

Link: https://lore.kernel.org/all/a68e65955e0df4db60233d468f348203c2e7b940.1651512451.git.geert+renesas@glider.be


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>