realtek: dts: fix Zyxel GS1920 port section

realtek: dts: fix Zyxel GS1920 port section

For the GS1920 the build system throws errors like

../dts/rtl8392_zyxel_gs1920-24hp-v1.dts:256.19-29:
Warning (reg_format): /switch@1b000000/ports/port@0:reg:
property has invalid length (4 bytes)
(#address-cells == 2, #size-cells == 1)

The dts misses the address and size properties for the
ports section. Fix that.

Fixes: 2a55846 ("realtek: add support for ZyXEL GS1920-24HPv1")
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/21534
Signed-off-by: Robert Marko <robimarko@gmail.com>