net: dsa: mv88e6xxx: Respect SPEED_UNFORCED, don't set force bit

The SPEED_UNFORCED indicates the MAC & PHY should perform
auto-negotiation to determine a speed which works. If this is called
for, don't set the force bit. If it is set, the MAC actually does
10Gbps, why the internal PHYs don't support.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/port.c

@@ -213,7 +213,7 @@ static int mv88e6xxx_port_set_speed(struct mv88e6xxx_chip *chip, int port,
 		reg &= ~PORT_PCS_CTRL_ALTSPEED;
 	if (force_bit) {
 		reg &= ~PORT_PCS_CTRL_FORCE_SPEED;
-		if (speed)
+		if (speed != SPEED_UNFORCED)
 			ctrl |= PORT_PCS_CTRL_FORCE_SPEED;
 	}
 	reg |= ctrl;