audio: mfcc: validate config blob size before use

[Shrusti-pk]

mfcc_prepare uses the config blob without checking it is long enough:

• the blob length comes from the bytes control and is only tested for non-zero
• mfcc_setup, the rest of prepare and the per-period processing code then read it as a 116-byte struct sof_mfcc_config, so a shorter blob is read past the end of its heap allocation
• mfcc registers no blob validator, unlike drc, eq_iir, tdfb and multiband_drc, so nothing rejects a short blob at IPC time either

Required the blob to cover the config struct, as drc_prepare does since d859e5d; the shipped mfcc blobs are all exactly 116 bytes so valid topologies are unaffected.

[sofci]

Can one of the admins verify this patch?

reply test this please to run this test once