perf tools: Collapse first level callchain entry if it has sibling

perf tools: Collapse first level callchain entry if it has sibling

If first level callchain has more than single path like when -g caller
option is given, it should show only first one in the path and hide
others.  But it didn't do it properly and just hindered the output.

Before:
  -   80.33%    11.11%  abc2     abc2              [.] main
     + 86.18% main
       13.82% __libc_start_main
          main

After:
  -   80.33%    11.11%  abc2     abc2              [.] main
     + 86.18% main
     + 13.82% __libc_start_main

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1416816807-6495-2-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>