[commit] Fix Xtensa-specific bug in MI command

[Joel Brobecker]

> Fix Xtensa-specific bug in MI command -data-list-changed-registers.

A small request: If you could give more details with your patches
about what you are fixing.  For the previous ones, there wasn't
much to add, just extending support for new features.  But for this
one, it would have been helpful to know what type of bug it was.
For instance, a transcript showing the issue can be useful to
other people hitting the problem, and doing an internet search.

-- 
Joel