net: phy: marvell: don't interpret PHY status unless resolved

Don't attempt to interpret the PHY specific status register unless
the PHY is indicating that the resolution is valid.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>