perf header: Fix numa topology printing

Andrew reported that the commit 7e94cfcc9d20 ("perf header: Use pre-
processed session env when printing") regresses the header output.  It
was because of a missed string pointer calculation in the loop.

Reported-by: Andrew Jones <drjones@redhat.com>
Tested-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andrew Jones <drjones@redhat.com>
Link: http://lkml.kernel.org/r/1350999890-6920-1-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>