perf stat: Fix per-pkg event reporting bug

Per-pkg events need to be captured once per processor socket. The code
in check_per_pkg() ensures only one value per processor package is used.
However there is a problem with this function in case the first CPU of
the package does not measure anything for the per-pkg event, but other
CPUs do.

Consider the following:

  $ create cgroup FOO; echo $$ >FOO/tasks; taskset -c 1 noploop &
  $ perf stat -a -I 1000 -e intel_cqm/llc_occupancy/ -G FOO sleep 100
    1.00000 <not counted> Bytes intel_cqm/llc_occupancy/  FOO

The reason for this is that CPU0 in the cgroup has nothing running on it.
Yet check_per_plg() will mark socket0 as processed and no other event
value will be considered for the socket.

This patch fixes the problem by having check_per_pkg() only consider
events which actually ran.

Signed-off-by: Stephane Eranian <eranian@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Kan Liang <kan.liang@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1441286620-10117-1-git-send-email-eranian@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>