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, 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:

(2 comments)

File stlinkv3_spi.c:

https://review.coreboot.org/c/flashrom/+/54042/comment/70f03beb_d17fa5d6 
PS1, Line 451: const
I've tried to fix this for good in CB:54066.

https://review.coreboot.org/c/flashrom/+/54042/comment/127a0ebc_66f6a239 
PS1, Line 351: 	struct stlinkv3_spi_data *stlinkv3_data = flash->mst->spi.data;
Adding a pointer for the handle would reduce some boilerplate below
and noise in the follow-up patch.