perf tools: Substitute yet another strtoull()

Instead of home grown function let's use what library provides us.

Signed-off-by: Andriy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/20180129130359.1490-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>