54c05828da413f6b4f9eec800a30624c453a4d90 introduced the printing of the
number of samples but on 64 bit macOS with clang the format specifier
generates warnings like:
stat.c:502:4: warning: format specifies type 'unsigned long' but the argument has type 'uint64_t'
(aka 'unsigned long long') [-Wformat]
(&ts->bw_stat[ddir])->samples);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Fix this by using the PRIu64 macro.
Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>