[M] Change in coreboot[main]: util/sconfig: Simplify file opening and error handling

[Nico Huber (Code Review)]

Attention is currently required from: Jakub Czapiga, Martin L Roth.

Nico Huber has posted comments on this change by Jakub Czapiga. ( https://review.coreboot.org/c/coreboot/+/70526?usp=email )

Change subject: util/sconfig: Simplify file opening and error handling
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Patch Set 5:

(2 comments)

File util/sconfig/main.c:

https://review.coreboot.org/c/coreboot/+/70526/comment/5049bcd5_05a9b6f0?usp... :
PS5, Line 2137: 		goto end;
Not sure why the compiler doesn't warn here. AIUI, this skips the initialization
of the other variables, hence we can't count on them being NULL. Individual jump
labels are the canonical way, I guess. i.e. `fclose()` in the reverse order and
let the first `goto` jump to the last `fclose()`, etc.

https://review.coreboot.org/c/coreboot/+/70526/comment/2abc8a9e_f7956ded?usp... :
PS5, Line 2183: 	return 0;
We shouldn't `return 0` on failure.