Continuous "fireCharacteristicUpdateCallback" errors on 5.2.0
# Expected Behavior
No errors in regular use.

### Current Behavior
Homebridge log displays continuous errors on three devices (one HS110, and two plugs on a HS300).

### Steps to Reproduce (for bugs)
Start homebridge, view logs.
<img width="1334" alt="image" src="https://user-images.githubusercontent.com/42701400/95932615-53622e00-0d9a-11eb-8493-f173fb2f8461.png">


### Versions
<!-- Please run commands and include versions below. -->
- **Node**:       12.18.1
- **Homebridge**: 1.2.3
- **OS**:       Homebridge Raspberry Pi Image

### Configuration
<!-- Please include the TplinkSmarthome platform section of your config.json file.
Paste between the the two ``` lines below.
-->
```json
    "name": "Kasa",
            "addCustomCharacteristics": false,
            "inUseThreshold": 60,
            "broadcast": "192.168.1.255",
            "pollingInterval": 10,
            "deviceTypes": [
                "plug",
                "bulb"
            ],
            "timeout": 1000,
            "transport": "udp",
            "platform": "TplinkSmarthome"
```

### Homebridge Log / Command Output
[10/13/2020, 21:25:50] [Kasa] [Noise Machine] fireCharacteristicUpdateCallback [0.46719600000000006]: Unable to call updateCallback VoltAmperes
[10/13/2020, 21:25:50] [Kasa] [Noise Machine] fireCharacteristicUpdateCallback [116.799]: Unable to call updateCallback Volts
[10/13/2020, 21:25:50] [Kasa] [Noise Machine] fireCharacteristicUpdateCallback [0.023]: Unable to call updateCallback Watts
[10/13/2020, 21:25:50] [Kasa] [Plug 6] fireCharacteristicUpdateCallback [0.011]: Unable to call updateCallback Amperes
[10/13/2020, 21:25:50] [Kasa] [Plug 6] fireCharacteristicUpdateCallback [0.019]: Unable to call updateCallback KilowattHours