hwmon: (w83795) Simplify temperature sensor type handling

All 3 temperature sensor type sysfs functions (show_temp_mode,
store_temp_mode and show_dts_mode) can be simplified. We don't
create these files when the correponding input isn't in temperature
monitoring mode, so there is no point in handling that case.
Likewise, we don't allow changing inputs from temperature to voltage,
so the code handling this case is dead and can be removed.

Signed-off-by: Jean Delvare <khali@linux-fr.org>