arm64: dts: renesas: beacon-renesom: Fix gpio expander reference

arm64: dts: renesas: beacon-renesom: Fix gpio expander reference

The board used to originally introduce the Beacon Embedded RZ/G2[M/N/H]
boards had a GPIO expander with address 20, but this was changed when
the final board went to production.

The production boards changed both the part itself and the address.
With the incorrect address, the LCD cannot come up.  If the LCD fails,
the rcar-du driver fails to come up, and that also breaks HDMI.

Pre-release board were not shipped to the general public, so it should
be safe to push this as a fix.  Anyone with a production board would
have video fail due to this GPIO expander change.

Fixes: a1d8a344f1ca ("arm64: dts: renesas: Introduce r8a774a1-beacon-rzg2m-kit")
Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230114225647.227972-1-aford173@gmail.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>