hwmon: (lm75) Modularize lm75_write and make hwmon_chip writable

* Create two separate functions to write into hwmon_temp and hwmon_chip.
* Call the functions from lm75_write.
* Make hwm_chip writable if the chip supports more than one sample time.

Signed-off-by: Iker Perez del Palomar Sustatxa <iker.perez@codethink.co.uk>
Link: https://lore.kernel.org/r/20190808080246.8371-5-iker.perez@codethink.co.uk


Signed-off-by: Guenter Roeck <linux@roeck-us.net>