net: dsa: mv88e6xxx: add delay in direct SMI wait

The mv88e6xxx_smi_direct_wait routine is used to wait on indirect
registers access. It is of no exception and must delay between read
attempts, like other wait routines.
Signed-off-by: Vivien Didelot <vivien.didelot@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/mv88e6xxx/smi.c

@@ -66,6 +66,8 @@ static int mv88e6xxx_smi_direct_wait(struct mv88e6xxx_chip *chip,
 
 		if (!!(data & BIT(bit)) == !!val)
 			return 0;
+
+		usleep_range(1000, 2000);
 	}
 
 	return -ETIMEDOUT;