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

[Edward O'Callaghan (Code Review)]

Attention is currently required from: Nico Huber, Angel Pons, Anastasia Klimchuk.
Edward O'Callaghan 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 3: Code-Review+1

(2 comments)

File buspirate_spi.c:

https://review.coreboot.org/c/flashrom/+/52958/comment/2867bc0d_94923a74 
PS3, Line 58: unsigned char **bp_commbuf
does this actually need double indirection?

https://review.coreboot.org/c/flashrom/+/52958/comment/67990204_dd146a96 
PS3, Line 221: unsigned char *const bp_commbuf = bp_data->bp_commbuf;
perhaps just move this up a few lines to the functions preamble so that the branch line above can be made shorter by using the itermediate.