hwmon: (dme1737) Prevent overflow problem when writing large limits

On platforms with sizeof(int) < sizeof(long), writing a temperature
limit larger than MAXINT will result in unpredictable limit values
written to the chip. Avoid auto-conversion from long to int to fix
the problem.

Voltage limits, fan minimum speed, pwm frequency, pwm ramp rate, and
other attributes have the same problem, fix them as well.

Zone temperature limits are signed, but were cached as u8, causing
unepected values to be reported for negative temperatures. Cache as
s8 to fix the problem.

vrm is an u8, so the written value needs to be limited to [0, 255].

Signed-off-by: Axel Lin <axel.lin@ingics.com>
[Guenter Roeck: Fix zone temperature cache]
Cc: stable@vger.kernel.org
Signed-off-by: Guenter Roeck <linux@roeck-us.net>