net: ravb: Remove writeext function call

The micrel phy driver is already configuring this values from
device tree. So remove the redundant phy configuration call from
this driver.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>