fix fallthrough on sample_channel_get on AQI

[KryQ]

There is a small bug present in ENS161 sensor driver where while getting samples for AQI logging return ERRNO -134
Cause was a lack of break in switch statement.

[github-actions]

Hello @KryQ, and thank you very much for your first pull request to the Zephyr project!
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[ubieda]

Thanks for your contribution!

[kartben]

@KryQ almost there with compliance check - please amend git author name/email to match the sign-off entry

[github-actions]

Hi @KryQ!
Congratulations on getting your very first Zephyr pull request merged 🎉🥳. This is a fantastic achievement, and we're thrilled to have you as part of our community!

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Thank you for your valuable input, and we look forward to seeing more of your contributions in the future! 🪁