selftests/resctrl: Remove unnecessary __u64 -> unsigned long conversion

Perf counters are __u64 but the code converts them to unsigned long
before printing them out.

Remove unnecessary type conversion and retain the perf originating
value as __u64.

Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>