util/hash-string: fix compile warning

Clang 19:

util-hash-string.c:41:16: error: implicit conversion loses integer precision: 'unsigned long' to 'int' [-Werror,-Wshorten-64-to-32]
   41 |     int len1 = strlen((char *)data1);
      |         ~~~~   ^~~~~~~~~~~~~~~~~~~~~
util-hash-string.c:42:16: error: implicit conversion loses integer precision: 'unsigned long' to 'int' [-Werror,-Wshorten-64-to-32]
   42 |     int len2 = strlen((char *)data2);
      |         ~~~~   ^~~~~~~~~~~~~~~~~~~~~
2 errors generated.

src/util-hash-string.c

@@ -38,8 +38,8 @@ uint32_t StringHashFunc(HashTable *ht, void *data, uint16_t datalen)
 char StringHashCompareFunc(void *data1, uint16_t datalen1,
                            void *data2, uint16_t datalen2)
 {
-    int len1 = strlen((char *)data1);
-    int len2 = strlen((char *)data2);
+    size_t len1 = strlen((char *)data1);
+    size_t len2 = strlen((char *)data2);
 
     if (len1 == len2 && memcmp(data1, data2, len1) == 0) {
         return 1;