Fix proximity issue

[titilambert]

Description:
Hello, I got the following error in my HA logs:

c 28 10:52:30 androlapin hass[9740]: ERROR:homeassistant.core:Error doing job: Future exception was never retrieved
Dec 28 10:52:30 androlapin hass[9740]: Traceback (most recent call last):
Dec 28 10:52:30 androlapin hass[9740]:   File "/usr/lib/python3.5/concurrent/futures/thread.py", line 55, in run
Dec 28 10:52:30 androlapin hass[9740]:     result = self.fn(*self.args, **self.kwargs)
Dec 28 10:52:30 androlapin hass[9740]:   File "/usr/local/lib/python3.5/dist-packages/homeassistant/components/proximity.py", line 145, in check_proximity_state_change
Dec 28 10:52:30 androlapin hass[9740]:     if devide_state is None:
Dec 28 10:52:30 androlapin hass[9740]: NameError: name 'devide_state' is not defined

This PR fixes this exception, I'm just not sure about the patch.

Checklist:

• Local tests with tox run successfully. Your PR cannot be merged unless tests pass

[mention-bot]

@titilambert, thanks for your PR! By analyzing the history of the files in this pull request, we identified @nickwaring, @fabaff and @balloob to be potential reviewers.

[pvizeli]

Thanks