Change in flashrom[master]: stlinkv3_spi.c: Refactor singleton states into reentrant pattern

[Nico Huber (Code Review)]

Attention is currently required from: Edward O'Callaghan, Angel Pons, Anastasia Klimchuk.
Nico Huber has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/54042 )

Change subject: stlinkv3_spi.c: Refactor singleton states into reentrant pattern
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Patch Set 1:

(1 comment)

File stlinkv3_spi.c:

https://review.coreboot.org/c/flashrom/+/54042/comment/aadf8a9f_251ffb76 
PS1, Line 533: stlinkv3_spi_open(sck_freq_kHz, stlinkv3_handle
> > > > Before this commit, the handle was closed unless register_shutdown() failed. […]

It's just the one more `goto err_exit` that you added (in case calloc
fails). It's one more case where resources are left open than before.
It's tiny compared to the other flaws around. So don't worry too much
about it.

I just realized there's even a double-libusb_exit() in case register_
spi_master() fails... and a new double-free() in this patch. So yes,
I think it's probably best to fix the error paths first. This change
would be easier to review if the code was sane already. I can also
fix things, it's more my fault that the code looks like this ;)