net: dsa: mv88e6xxx: fix 6085 frame mode masking

The register bits used for the frame mode were masked with DSA (0x1)
instead of the mask value (0x3) in the 6085 implementation of
port_set_frame_mode. Fix this.

Fixes: 56995cbc ("net: dsa: mv88e6xxx: Refactor CPU and DSA port setup")
Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/port.c

@@ -451,7 +451,7 @@ int mv88e6085_port_set_frame_mode(struct mv88e6xxx_chip *chip, int port,
 	if (err)
 		return err;
 
-	reg &= ~PORT_CONTROL_FRAME_MODE_DSA;
+	reg &= ~PORT_CONTROL_FRAME_MASK;
 
 	switch (mode) {
 	case MV88E6XXX_FRAME_MODE_NORMAL: