ar1021_i2c also supports the ar1020 device I'm using. This is tested.
They also share the same datasheet:

   http://ww1.microchip.com/downloads/en/DeviceDoc/40001393C.pdf

So let users see that they have a compatible in front of them by adding
AR1020 to the driver's description.
Signed-off-by: Martin Kepplinger <martin.kepplinger@ginzinger.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>