It can't be set up to 0 ohm, even if you write the minimum value 00h to register 02h/03h, the typical position 0's resistor is 160 ohm.
DS3902
Not Recommended for New Designs
The DS3902 features a dual, nonvolatile (NV), low temperature-coefficient, variable digital resistor with 256 user-selectable positions. The DS3902 can...
Datasheet
DS3902 on Analog.com