Fix: MSPM0 cleanup

[dragonmux]

Detailed description

This PR does some post-initial-PR cleanup for clang-tidy lints and small pattern issues that do not change functionality of the implementation but do improve code size and consistency a little. Nothing too huge - the implementation could still do with having the mass erase function refactored into a bank erase function and registered as flash->mass_erase rather than target->mass_erase, but without a part to test that against we're unwilling to go changing that for the moment.

Your checklist for this pull request

• I've read the Code of Conduct
• I've read the guidelines for contributing to this repository
• It builds for hardware native (see Building the firmware)
• It builds as BMDA (see Building the BMDA)
• I've tested it to the best of my ability
• My commit messages provide a useful short description of what the commits do

Closing issues

[esden]

LGTM