arm64: dts: renesas: r8a779a0: Update CAN-FD to R-Car Gen4 compatible value

Despite the name, R-Car V3U is the first member of the R-Car Gen4
family.  Hence update the compatible property in the CAN-FD device node
to include the family-specific compatible value for R-Car Gen4.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/9823058fa57156e88a084a4a99fc8525af1686ff.1678705389.git.geert+renesas@glider.be