hwmon: (nct6775) Fix temperature alarm attributes

Driver displays wrong alarms for temperature attributes.

Turns out that temperature alarm bits are not fixed, but determined
by temperature source mapping. To fix the problem, walk through
the temperature sources to determine the correct alarm bit associated
with a given attribute.

Cc: stable@vger.kernel.org # 3.10+
Signed-off-by: Guenter Roeck <linux@roeck-us.net>