ravb: remove useless serialization in ravb_get_link_ksettings()

phy_ethtool_ksettings_get() call does not modify device state or device
driver state, hence there is no need to utilize a driver specific
spinlock.

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>