Change in flashrom[master]: programmer: Smoothen register_spi_master() API

[Anastasia Klimchuk (Code Review)]

Attention is currently required from: Nico Huber, Edward O'Callaghan.
Anastasia Klimchuk has posted comments on this change. ( https://review.coreboot.org/c/flashrom/+/54066 )

Change subject: programmer: Smoothen register_spi_master() API
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Patch Set 1: Code-Review+1

(1 comment)

File spi.c:

https://review.coreboot.org/c/flashrom/+/54066/comment/f157fcea_1f0e2c50 
PS1, Line 151: 	if (data)
             : 		rmst.spi.data = data;
This would need to move to register_master at some point, because the same situation exists now for par_master and opaque_master.
Means, we need similar patch for register_par_master/opaque which changes the callsites in the tree. And then later internal change to move these two lines into register_master?
For par masters, I haven't started refactoring them, maybe it's a good time to intro a patch like this for par masters? Do you mind if I do it or would you like to do it?

Anyway, thank you!