selftests/cachestat: Fix print_cachestat format

Compiling cachestat selftest after adding a __printf() attribute to
ksft_print_msg() exposes a -Wformat warning in print_cachestat().
The format specifier in printf() call expects long int variables and
received long long int.

Change format specifiers to long long int so they match passed
variables.

Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>