arm64: dts: armada-3720-turris-mox: Correct reg property for mdio devices

MDIO devices have #address-cells = <1>, #size-cells = <0>. Now that we
have a schema enforcing this for marvell,orion-mdio we can see that the
turris-mox has a unnecessary 2nd cell for the switch nodes reg property
of it's switch devices. Remove the unnecessary 2nd cell from the
switches reg property.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reviewed-by: Marek Behún <kabel@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>