net: phy: marvell: fix downshift function naming

I got access to the M88E1111 datasheet, and this PHY version uses
another register for downshift configuration. Therefore change prefix
to m88e1011, aligned with constants like MII_M1011_PHY_SCR.

Fixes: a3bdfce7

 ("net: phy: marvell: support downshift as PHY tunable")
Reported-by: Chris Healy <Chris.Healy@zii.aero>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>