logopenfile: fix minor format string warning

logopenfile: fix minor format string warning

cppcheck:

src/util-logopenfile.c:743:13: warning: %d in format string (no. 2) requires 'int' but the argument type is 'unsigned int'. [invalidPrintfArgType_sint]
            snprintf(threaded_name, len, "%s.%d.%s", tname, unique_id, ext);
            ^
src/util-logopenfile.c:752:9: warning: %d in format string (no. 2) requires 'int' but the argument type is 'unsigned int'. [invalidPrintfArgType_sint]
        snprintf(threaded_name, len, "%s.%d", original_name, unique_id);
        ^

Bug: #5291.