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].

(cherry picked from commit b53a809)
(cherry picked from commit 3cc2aa3)

Author: huyubiao

src/shared/hwdb-util.c

@@ -193,7 +193,7 @@ static int trie_insert(struct trie *trie, struct trie_node *node, const char *se
 
         for (size_t i = 0;; i++) {
                 size_t p;
-                uint8_t c;
+                char c;
                 struct trie_node *child;
 
                 for (p = 0; (c = trie->strings->buf[node->prefix_off + p]); p++) {