dt-bindings: net: marvell,orion-mdio: Set unevaluatedProperties to false

When the binding was converted it appeared necessary to set
'unevaluatedProperties: true' because of the switch devices on the
turris-mox board. Actually the error was because of the reg property
being incorrect causing the rest of the properties to be unevaluated.

After the reg properties are fixed for turris-mox we can set
'unevaluatedProperties: false' as is generally expected.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>