fix: use of cpu in demos

[rogeherlor]

The original code raised an exception when only using CPU. In this way I could run the demos

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[saratpoluri]

@rogeherlor : can you please resolve conflicts for this PR.

[saratpoluri]

@facebook-github-bot : can you please assign a reviewer with merge privileges. The changes work on my system.

[saratpoluri]

@jytime : could you please review and merge this. Thanks.