net: phy: micrel: set soft_reset callback to genphy_soft_reset for KSZ9031

So far genphy_soft_reset was used automatically if the PHY driver
didn't implement the soft_reset callback. This changed with the
mentioned commit and broke KSZ9031. To fix this configure the
KSZ9031 PHY driver to use genphy_soft_reset.

Fixes: 6e2d85ec ("net: phy: Stop with excessive soft reset")
Reported-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Tested-by: Tony Lindgren <tony@atomide.com>
Tested-by: Sekhar Nori <nsekhar@ti.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>