test/fd-pass: use unsigned char for pattern check range
@@ -22,7 +22,7 @@ static int verify_fixed_read(struct io_uring *ring, int fixed_fd, int fail)
{
struct io_uring_sqe *sqe;
struct io_uring_cqe *cqe;
- char buf[FSIZE];
+ unsigned char buf[FSIZE];
int i;
sqe = io_uring_get_sqe(ring);
