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

[Angel Pons (Code Review)]

Attention is currently required from: Nico Huber, Edward O'Callaghan, Anastasia Klimchuk.
Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/52958 )

Change subject: buspirate_spi.c: Refactor singleton states into reentrant pattern
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Patch Set 2:

(1 comment)

File buspirate_spi.c:

https://review.coreboot.org/c/flashrom/+/52958/comment/fb9bb438_d943e1bd 
PS2, Line 167: 	struct buspirate_spi_data *buspirate_data = data;
> Thank you for this comment, because I started resolving it and so spent some more time staring at th […]

bp_commbuf was global to minimize the number of times one needs to call malloc() or realloc(). There's a comment in buspirate_commbuf_grow() that gives a hint:

/* Never shrink. realloc() calls are expensive. */