perf stat: Fix --per-core on multi socket systems

On systems with more than one socket perf stat --per-core would either
segfault or stop before outputting all cores.

The problem was that the output code referenced the id including the
socket number in the higher bits, which is far beyond any per cpu array.

Mask out the socket number before referencing cpus in abs_printout.

I also renamed the variable in nsec_printout to be clear what it is,
even though it doesn't reference cpus.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Stephane Eranian <eranian@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1411591846-32736-1-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>