dt-bindings: net: toshiba,visconti-dwmac: Update the common clock properties

The clock for this driver switched to the common clock controller driver.
Therefore, update common clock properties for ethernet device in the binding
document.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>