systemd-hwdb: fix unsigned and signed comparison problem

systemd-hwdb: fix unsigned and signed comparison problem
...
uint8_t c;
struct trie_node *child;

for (p = 0; (c = trie->strings->buf[node->prefix_off + p]); p++) {
        _cleanup_free_ struct trie_node *new_child = NULL;
        _cleanup_free_ char *s = NULL;
        ssize_t off;
if (c == search[i + p])
        continue;
...
When '®' is present in search, c is 194, search[i + p] is -62, c is not equal to search[i + p], but c should be equal to search[i + p].