eq3btsmart: add reporting for availability (home-assistant#5594)

* eq3btsmart: add reporting for availability

* Update eq3btsmart.py

Author: rytilahti

homeassistant/components/climate/eq3btsmart.py

@@ -76,6 +76,11 @@ def __init__(self, _mac, _name):
         self._name = _name
         self._thermostat = eq3.Thermostat(_mac)
 
+    @property
+    def available(self) -> bool:
+        """Return if thermostat is available."""
+        return self.current_operation != STATE_UNKNOWN
+
     @property
     def name(self):
         """Return the name of the device."""