Fix type used.

`char` seems to be `unsigned` by default on aarch64, therefore use `int8_t`
instead.

This fixes #591
Reported via DCIT/perl-CryptX#121

Fixes: 3cdcec4 ("first batch of simplifications")

Signed-off-by: Steffen Jaeckel <[email protected]>

Author: sjaeckel

mp_kronecker.c

@@ -23,7 +23,7 @@ mp_err mp_kronecker(const mp_int *a, const mp_int *p, int *c)
    mp_err err;
    int v, k;
 
-   static const char table[] = {0, 1, 0, -1, 0, -1, 0, 1};
+   static const int8_t table[] = {0, 1, 0, -1, 0, -1, 0, 1};
 
    if (mp_iszero(p)) {
       if ((a->used == 1) && (a->dp[0] == 1u)) {