[Gotthard2][Correct] Add `idx` to `da_to_pdu` to use in picking correct `data_source`

Description

This is a proper fix for picking the correct data source for GH2 25um modules.

This is to avoid the developed temporary workaround. !955 (merged)

How Has This Been Tested?

Relevant Documents (optional)

hirex_gh2_correct.pdf

hirex_gh2_dark.pdf

fxe_gh2_correct.pdf

fxe_gh2_dark.pdf

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

Reviewers

@schmidtp @kluyvert