mpi/ec: remove VLA usage
* mpi/ec-nist.c (_gcry_mpi_ec_nist192_mod, _gcry_mpi_ec_nist224_mod) (_gcry_mpi_ec_nist256_mod, _gcry_mpi_ec_nist384_mod) (_gcry_mpi_ec_nist521_mod): Avoid VLA for arrays. * mpi/ec.c (ec_secp256k1_mod): Avoid VLA for arrays.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>