arm64: dts: marvell: fix watchdog unit address in Armada AP806

This fixes the following DTC warning:

  Warning (simple_bus_reg): Node /ap806/config-space@f0000000/watchdog@600000 simple-bus unit address format error, expected "610000"

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>