hwmon: I2C addresses are constant

We can mark normal_i2c const. Almost all drivers do that already, so
fix the 3 remaining ones before they are used as (bad) examples for
new drivers.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: George Joseph <george.joseph@fairview5.com>
Reviewed-by: Guenter Roeck <guenter.roeck@ericsson.com>