net: phy: dp83867: fix speed 10 in sgmii mode

commit 333061b9 upstream.

For supporting 10Mps speed in SGMII mode DP83867_10M_SGMII_RATE_ADAPT bit
of DP83867_10M_SGMII_CFG register has to be cleared by software.
That does not affect speeds 100 and 1000 so can be done on init.

Signed-off-by: Max Uvarov <muvarov@gmail.com>
Cc: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[ adapted for kernels without phy_modify_mmd ]
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>