docs: fix CURLINFO_*_T examples use of CURL_FORMAT_CURL_OFF_T

- Put a percent sign before each CURL_FORMAT_CURL_OFF_T in printf.

For example "%" CURL_FORMAT_CURL_OFF_T becomes %lld or similar.

Bug: https://curl.haxx.se/mail/lib-2018-03/0140.html
Reported-by: David L.