hwmon: (it87) Fix thermal sensor type values

The it87 driver doesn't follow the standard sensor type values as
documented in Documentation/hwmon/sysfs-interface. It uses value 2 for
thermistors instead of value 4. This causes "sensors" to tell the user
that the chip is setup for a transistor while it is actually setup for
a thermistor.

Using value 4 for thermistors solves the problem. For compatibility
reasons, we still accept value 2 but emit a warning message so that
users update their configuration files.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Acked-by: Hans de Goede <hdegoede@redhat.com>