perf hists browser: Fix a small callchain display bug

perf hists browser: Fix a small callchain display bug

The currently when perf TUI report shows callchain, the first level
chains have bogus '+' sign even though only the last one has children.

Since they are on a single line of the chain, toggling intermediate
entries has no effect.  Fix it to show '+' sign at the last entry only.
Note that non-first level callchain entries don't have this problem.

  Before:
  ---------------------------------------------------------------------------
    Children      Self  Command  Shared Object      Symbols
  -   40.70%     0.00%  swapper  [kernel.kallsyms]  [k] cpuidle_wrap_enter
     + cpuidle_wrap_enter
     + cpuidle_enter_tk
     + cpuidle_idle_call
     + cpu_idle

  After:
  ---------------------------------------------------------------------------
    Children      Self  Command  Shared Object      Symbols
  -   40.70%     0.00%  swapper  [kernel.kallsyms]  [k] cpuidle_wrap_enter
       cpuidle_wrap_enter
       cpuidle_enter_tk
       cpuidle_idle_call
     + cpu_idle

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
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>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Link: http://lkml.kernel.org/r/1407909761-10822-1-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>