Xiaomi Aqara: Don't call async from sync

[balloob]

Description:

Call sync version of register.

Found by @arsaboo after running asyncio in debug mode via hass.loop.set_debug(True):

Error during setup of component xiaomi_aqara
Traceback (most recent call last):
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/setup.py", line 145, in _async_setup_component
    component.setup, hass, processed_config)
  File "/usr/lib/python3.6/asyncio/futures.py", line 332, in __iter__
    yield self  # This tells Task to wait for completion.
  File "/usr/lib/python3.6/asyncio/tasks.py", line 250, in _wakeup
    future.result()
  File "/usr/lib/python3.6/asyncio/futures.py", line 245, in result
    raise self._exception
  File "/usr/lib/python3.6/concurrent/futures/thread.py", line 56, in run
    result = self.fn(*self.args, **self.kwargs)
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/components/xiaomi_aqara.py", line 187, in setup
    schema=_add_gateway_to_schema(xiaomi, SERVICE_SCHEMA_PLAY_RINGTONE))
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/core.py", line 861, in async_register
    {ATTR_DOMAIN: domain, ATTR_SERVICE: service}
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/core.py", line 409, in async_fire
    self._hass.async_add_job(func, event)
  File "/srv/homeassistant/lib/python3.6/site-packages/homeassistant/core.py", line 220, in async_add_job
    self.loop.call_soon(target, *args)
  File "/usr/lib/python3.6/asyncio/base_events.py", line 576, in call_soon
    self._check_thread()
  File "/usr/lib/python3.6/asyncio/base_events.py", line 615, in _check_thread
    "Non-thread-safe operation invoked on an event loop other "
RuntimeError: Non-thread-safe operation invoked on an event loop other than the current one

[OttoWinter]

Oh, that option is very handy! Good to know 👍 (I'll put it on my staging server to hopefully catch a few more of these)

[balloob]

@OttoWinter went 1 step further and enabled it for all our tests #13058