hwmon: (lm90) Fix max6696 alarm handling

Bit 2 of status register 2 on MAX6696 (external diode 2 open)
sets ALERT; the bit thus has to be listed in alert_alarms.
Also display a message in the alert handler if the condition
is encountered.

Even though not all overtemperature conditions cause ALERT
to be set, we should not ignore them in the alert handler.
Display messages for all out-of-range conditions.

Reported-by: Jean Delvare <khali@linux-fr.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Cc: stable@vger.kernel.org
Signed-off-by: Jean Delvare <khali@linux-fr.org>