Cellular: Fix bc95 to accept only RAT_NB1

[jarvte]

Fixed TODO comment by correct implementation:

RAT_NB1 is the only rat that bc95 supports so this fix prevents changing it some other.

@AriParkkila please review

Pull request type

[X] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[0xc0170]

Note about the 1st line commit length (review how Github displayes it and git log - how it wraps), ideally first commit line 50 char

[0xc0170]

Info: This PR has been re-bundled into a new rollup PR (#8862).

No further work is needed here, as once that PR is merged, this PR will also be closed and marked as merged.
If any more commits are made in this PR, this PR will remain open and have to go through CI on its own.