ARM: dts: dra71-evm: mdio: Fix impedance values

ARM: dts: dra71-evm: mdio: Fix impedance values

v1 series[1] for dp83867 phy impedance-control support,
specifies to use ti,impedance-control with a value. These
properties got updated iduring review to specify whether
min or max impedance. But the DT still uses the old values
which never takes effect. Update the DT node by using the
proper DT properties.

[1] https://patchwork.kernel.org/patch/9239729/

Fixes: 9868bc585ae2c ("ARM: dts: Add support for dra718-evm")
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>