Fix zwave_js sensor device class attribute error

[MartinHjelmare]

Breaking change

Proposed change

• The value property_ attribute can be a number or a string.
• https://zwave-js.github.io/node-zwave-js/#/api/valueid

2021-02-02 14:04:10 ERROR (MainThread) [homeassistant.components.sensor] Error adding entities for domain sensor with platform zwave_js
Traceback (most recent call last):
  File "/home/martin/dev/home-assistant/core/homeassistant/helpers/entity_platform.py", line 315, in async_add_entities
    await asyncio.gather(*tasks)
  File "/home/martin/dev/home-assistant/core/homeassistant/helpers/entity_platform.py", line 423, in _async_add_entity
    device_class=entity.device_class,
  File "/home/martin/dev/home-assistant/core/homeassistant/components/zwave_js/sensor.py", line 76, in device_class
    if "temperature" in self.info.primary_value.property_.lower():
AttributeError: 'int' object has no attribute 'lower'

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[raman325]

👍🏾

[balloob]

This looks good. For another PR, is this something that we can compute when we instantiate the class instead on each time we read this property?