dsa: mv88e6xxx: Make mv88e6xxx_wait() timeout verbose

When mv88e6xxx_wait() returns a timeout, something bad has
happened. Make sure it is noticed by logging an error.
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/chip.c

@@ -325,6 +325,7 @@ static int mv88e6xxx_wait(struct mv88e6xxx_chip *chip, int addr, int reg,
 		usleep_range(1000, 2000);
 	}
 
+	dev_err(chip->dev, "Timeout while waiting for switch\n");
 	return -ETIMEDOUT;
 }