perf ui/stdio: Fix invalid output on event group report

When some of group member has 0 overhead, it printed previous percentage
instead of 0.00%.  It's because passing integer 0 as a percent rather
than double 0.0 so the remaining bits came from garbage.  The TUI and
GTK don't have this problem since they pass 0.0.

Before:

  # Samples: 845  of event 'anon group { cycles, cache-references, cache-misses }'
  # Event count (approx.): 174775051
  #
  #                 Overhead                               Samples
  # ........................  ....................................
  #
      20.32%   8.58%  73.51%            45          30         138
       6.87%   6.87%   6.87%            21           0           0
       5.29%   0.31%   0.31%            10           1           0
       1.89%   1.89%   1.89%             6           0           0
       1.76%   1.76%   1.76%             2           0           0

After:

  #                 Overhead                               Samples
  # ........................  ....................................
  #
      20.32%   8.58%  73.51%            45          30         138
       6.87%   0.00%   0.00%            21           0           0
       5.29%   0.31%   0.00%            10           1           0
       1.89%   0.00%   0.00%             6           0           0
       1.76%   0.00%   0.00%             2           0           0

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@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/1393809254-4480-2-git-send-email-namhyung@kernel.org


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