mceliece6688128f: use const-time helper for memory comparison
* cipher/mceliece6688128f.c (sync_cmp): Use const-time helper for comparison.
Cherry-pick master commit of:
4c253746e52020254ede4f41d0440b41ca3aa8ec
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>