arm64: dts: realtek: Clean up RTD1295 UART reg property

The downstream RTD1195 and apparently RTD1295 trees have a modified 8250
serial driver that acknowledges its interrupts using the second reg area,
which is an irq mux.

Drop these unused second reg entries for the UART nodes.

Fixes: 72a7786c0a0d ("ARM64: dts: Add Realtek RTD1295 and Zidoo X9S")
Signed-off-by: Andreas Färber <afaerber@suse.de>