net: phy: vitesse: repair vsc73xx autonegotiation

[ Upstream commit de7a670f8defe4ed2115552ad23dea0f432f7be4 ]

When the vsc73xx mdio bus work properly, the generic autonegotiation
configuration works well.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Pawel Dembicki <paweldembicki@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>