Offset calculation fix for etdump (#1365)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1365

Caught a bug in the offset calculation while integrating etdump into the Xtensa workflows. This only shows up when the base address itself is not 64 bytes aligned.

Also changed the name of `buffer_path` to `debug_buffer_path` in inspector.py

Reviewed By: Gasoonjia

Differential Revision: D51913391

fbshipit-source-id: cfa0ffc7878ceb0f62db22061f3ed326cce211a0