ravb: simplify link auto-negotiation by ethtool

There is no need to call a heavyweight phy_start_aneg() for phy
auto-negotiation by ethtool, the phy is already initialized and
link auto-negotiation is started by calling phy_start() from
ravb_phy_start() when a network device is opened.

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Reviewed-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>