[S] Change in coreboot[master]: vboot: Fix hash digest size, padding and comparison

[Yu-Ping Wu (Code Review)]

Attention is currently required from: Jakub Czapiga, Caveh Jalali, Julius Werner, Boris Mittelberg.

Yu-Ping Wu has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/69762 )

Change subject: vboot: Fix hash digest size, padding and comparison
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Patch Set 3:

(2 comments)

File src/ec/google/chromeec/vboot_storage.c:

https://review.coreboot.org/c/coreboot/+/69762/comment/b1648d64_42dc3fbc 
PS2, Line 21: memset(data, 0, sizeof(data));
> There is a slot number check and max data size check. […]

With
```
struct ec_params_vstore_write req = {
    .slot         = slot,
};
```

I think the unspecified field `.data` will be zero.

https://review.coreboot.org/c/coreboot/+/69762/comment/e509ad7b_8980e755 
PS2, Line 50: 	assert(digest_size == EC_VSTORE_SLOT_SIZE);
> It has to stay. […]

Right.