perf evsel: Set leader evsel's ->leader to itself

Currently only non-leader members are set ->leader to the leader evsel
of the group and the leader has set NULL.  Thus it requires special
casing for leader evsels.  Set ->leader to itself will remove this.

Suggested-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/1354171126-14387-3-git-send-email-namhyung@kernel.org


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