perf sort: Fix --sort pid output

The "pid" sort key prints "Command: Pid" output but it's misaligned.
It's because of the offset of 6 was added to the column length during
the calculation in order to reserve an space for Pid part but it isn't
honored when printed.  The output before this patch was like this:

  # Overhead  Command:  Pid      Shared Object
  # ........  .............  .................
  #
      99.70%        noploop:17814  noploop
       0.29%        noploop:17814  [kernel.kallsyms]
       0.01%        noploop:17814  ld-2.15.so

Fix it by subtracting 6 for printing comm part.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
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/1356599507-14226-4-git-send-email-namhyung@kernel.org


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