Change in flashrom[master]: programmer: Introduce default shutdown function

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Nico Huber, Edward O'Callaghan, Angel Pons.
Anastasia Klimchuk has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/54890 )

Change subject: programmer: Introduce default shutdown function
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Patch Set 5:

(1 comment)

File flashrom.c:

https://review.coreboot.org/c/flashrom/+/54890/comment/f12c329b_565f932c 
PS5, Line 104: function;
> I'd much prefer to return an error if one calls `register_shutdown()` with a null function pointer.

Yes, when I mentioned "shutdown function should be required" above, in my mind it was exactly this: checking that shutdown function is not null and return a error if it is. So that the caller has to give a function. And this default shutdown function would be for convenience, for those callers that don't need anything custom on shutdown.