imgtool: dumpinfo.py: use correct define when tlv iterating

[bravl]

When iterating over tlv's the TLV_SIZE should be used and not TLV_INFO_SIZE.

[jacmet]

Maybe mention that this is just for clarity as both are the same value (4)

[github-actions[bot]]

This pull request has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this pull request will automatically be closed in 14 days. Note, that you can always re-open a closed pull request at any time.

[jacmet]

Ping? This is AFAIK still applicable. Please drop the stale label