arm64: dts: renesas: beacon: Correct I2C bus speeds

For greater compatibility with upcoming kits that will reuse the baseboard
and SOM-level files, adjust the I2C speeds to make it the most compatible
with all devices.

Signed-off-by: Adam Ford <aford173@gmail.com>
Link: https://lore.kernel.org/r/20201213183759.223246-15-aford173@gmail.com


Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>