Michael Ellerman is between a rock and a hard place here: he
could have done better and that's something that may have to be added to the guidelines for the patch contributors, at the same time maintainers have a massive workload and this was a tiny, broken patch submitted in a non-standard way by a new contributor. He
could have made the origins of the few lines of code clearer but maintainers do this all the time, they usually are more focused on the quality of the code, and getting
a fix in (even if it isn't yours) and may not realize that the contribution is insignificant compared to the fact that someone is very much focused on the credit.
Incentives clearly aren't aligned and I think if the OP would have taken this up privately they could have worked it out. Instead you get this public attack on people that we already have far too few of and one that misrepresents the interaction. That's where I draw the line: you keep your dirty laundry inside until you've exhausted every avenue for redress if you really care that much. Note that Ellerman explicitly offered to work with the OP if he wanted to be credited for a patch to the kernel on another bug, which is one way to differentiate between drive-by contributors and long term relationships.
All in all I think everybody could have done better here but Michael Ellerman's wrongs are far less clear to me than what the OP did and I'm fairly sure if there had been a ready for inclusion patch or better guidelines about how to deal with various degrees of crediting contributors (and probably for a more substantial fix) that there would have been no problem either.
Personally I don't see the problem at all: the LKML thread is archived for eternity, the contribution of the OP is clear, if he wants to say he's contributed code to the kernel I don't think anybody would object to that and Ellerman did his job as a maintainer, even if he could have handled it with some more grace I'm more than willing to forgive him. If I had been in the OPs place I would have probably jumped at the opportunity suggested by the invitation, and I definitely would not have 'paraphrased' the interaction or use the word 'robbed' without first reaching out to Michael Ellerman because those two things alone undo any goodwill created by the submission of the patch.