Fix Canary KeyError: 'ffmpeg_arguments'

[frenck]

Proposed change

Fixes Canary KeyError during setup.

        Traceback (most recent call last):
          File "/home/lee/homeassistant/lib/python3.7/site-packages/homeassistant/helpers/entity_platform.py", line 178, in _async_setup_platform
            await asyncio.wait_for(asyncio.shield(task), SLOW_SETUP_MAX_WAIT)
          File "/usr/lib/python3.7/asyncio/tasks.py", line 442, in wait_for
            return fut.result()
          File "/usr/lib/python3.7/concurrent/futures/thread.py", line 57, in run
            result = self.fn(*self.args, **self.kwargs)
          File "/home/lee/homeassistant/lib/python3.7/site-packages/homeassistant/components/canary/camera.py", line 45, in setup_platform
            config[CONF_FFMPEG_ARGUMENTS],
        KeyError: 'ffmpeg_arguments'

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
• New feature (which adds functionality to an existing integration)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

Example entry for configuration.yaml:

# Example configuration.yaml

Additional information

• This PR fixes or closes issue: fixes Error while setting up canary platform for camera #35157
• This PR is related to issue:
• Link to documentation pull request:

Checklist

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