perf hists: Move column length calculation out of hists__inc_stats()

It's not the part of logic of hists__inc_stats() so it'd be better to
move it out of the function.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/1398327843-31845-4-git-send-email-namhyung@kernel.org


Signed-off-by: Jiri Olsa <jolsa@kernel.org>