arm64: dts: lx2160a-rdb: fix shunt-resistor value

Fix value of shunt-resistor property.
The LX2160A-RDB has 500 uOhm shunt for
the INA220, not 1000 uOhm. Unless
it will get wrong power consumption(1/2)

Signed-off-by: Biwen Li <biwen.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>