net: netcp: ethss: get phy-handle only if link interface is MAC-to-PHY

Currently to parse phy-handle, driver doesn't check if the interface is
MAC to PHY. This patch add this check for all MAC to PHY interface types
supported by the driver.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>