Use common strings for somfy config flow

[RobBie1221]

Breaking change

Proposed change

Fix two more instances where common strings can be used.

See #40578

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# Example configuration.yaml

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[probot-home-assistant]

Hey there @tetienne, mind taking a look at this pull request as its been labeled with an integration (somfy) you are listed as a codeowner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[springstan]

Thanks!