Air purifier H7122: no fan speed control
### What issue do you have? Please be as thorough and explicit as possible.

Issue
When I change the fan speed slider in the Home App the air purifier selects “custom” fan speed for fan speeds <= 75% and auto mode for fan speeds greater than 75%


Expected 
Fan speeds 1, 2 and 3 are selected based on the appropriate fan speed slider position  in the Home App

### Details of your setup.
* Do you use Homebridge (with config-ui?) or HOOBS? 

Homebridge running on macOS with config-ui

* Which version of Homebridge/HOOBS do you have?

1.5.0

* Which version of this plugin (homebridge-govee) do you have? Has the issue started since upgrading from a previous version?

5.2.0

* Which Govee devices do you have that are causing issues? Please include product models if applicable.

Air purifier h7122


