perf stat: Introduce get_ratio_color() helper

The get_ratio_color() returns appropriate color string based on @ratio.
It helps reducing code duplication.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1325000151-4463-2-git-send-email-namhyung@gmail.com


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