perf ui/gtk: Fix segmentation fault on perf_hpp__for_each_format loop

perf ui/gtk: Fix segmentation fault on perf_hpp__for_each_format loop

The commit 2b8bfa6bb8a7 ("perf tools: Centralize default columns init in
perf_hpp__init") moves initialization of common overhead column to
perf_hpp__init() but forgot about the gtk code.

So the gtk code added the same column to the list twice causing infinite
loop when iterating it by perf_hpp__for_each_format loop.  When I run
perf report --gtk, I can see following messages indefinitely.

  (perf:11687): Gtk-CRITICAL **: IA__gtk_main_quit: assertion 'main_loops != NULL' failed
  perf: Segmentation fault

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Reviewed-by: Pekka Enberg <penberg@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1375766056-19377-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>