MSS620 - Multi channel device not functioning
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### What issue do you have? Please be as thorough and explicit as possible.
MSS620 switch stopped functioning after recent update


### Details of your setup.
* Do you use (1) Homebridge UI-X (2) Homebridge CLI or (3) HOOBS? 

(1)

* Which version of Homebridge/HOOBS do you have?

Homebridge v1.3.4 

* Which platform do you run Homebridge/HOOBS on (e.g. Raspberry Pi/Windows/HOOBS Box)? Please also mention your version of Node.js/NPM if known.

VirtualBox - Ubuntu
Linux homebridge 4.15.0-151-generic #157-Ubuntu SMP Fri Jul 9 23:07:57 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux


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

homebridge-meross v6.8.0 

Yes, issue started after upgrading from v6.7.1 or v6.7.2 (didn't noticed but was functional on v6.x)

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

MSS620

### Please paste any relevant logs below.
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```
[8/24/2021, 10:00:10 PM] [Meross] [Insect Trap SW1] has been added to Homebridge.
[8/24/2021, 10:00:10 PM] [Meross] [Insect Trap SW1] initialising with options {"connection":"local","hideChannels":"0","logging":"standard","showAs":"outlet"}.
[8/24/2021, 10:00:11 PM] [Meross] [Insect Trap SW2] has been added to Homebridge.
[8/24/2021, 10:00:11 PM] [Meross] [Insect Trap SW2] initialising with options {"connection":"local","hideChannels":"0","logging":"standard","showAs":"outlet"}.
[8/24/2021, 10:00:11 PM] [Meross] [Insect Trap SW2] could not be initialised as Cannot read property 'displayName' of undefined at MerossPlatform.initialiseDevice (/usr/lib/node_modules/homebridge-meross/lib/index.js:699:43).
```
