Hardware MPI loses sign when multiplying by -1

[pieceofsummer]

Test case:

mbedtls_mpi x, y, z;
mbedtls_mpi_init(&x); mbedtls_mpi_init(&y); mbedtls_mpi_init(&z);

mbedtls_mpi_lset(&x, 12345);
mbedtls_mpi_lset(&y, -1);
mbedtls_mpi_mul_mpi(&z, &x, &y);

mbedtls_mpi_write_file(NULL, &z, 10, NULL);

Expected: -12345
Actual: 12345

[CLAassistant]

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[projectgus]

Good catch @pieceofsummer , thank you. I've pushed this into our internal review & merge queue.