hwmon: (pmbus) Continuously update temperature limit registers

PMBus only has one set of limit registers for up to three temperature sensors.
Thus, changing a limit for one of the temperature sensors affects limits for
other temperature sensors in the same page (and potentially multiple pages
depending on the chip implementation). To handle this situation, re-read all
temperature limit registers when updating sensor data. This way, all affected
temperature limits are updated whenever the limit for a single sensor is
changed.

Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>