perf hists: Update hists' total period when adding entries

Currently the hist entry addition path doesn't update total_period of
hists and it's calculated during 'resort' path.  But the resort path
needs to know the total period before doing its job because it's used
for calculating percent limit of callchains in hist entries.

So this patch update the total period during the addition path.  It
makes the percent limit of callchains working (again).

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1453909257-26015-3-git-send-email-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>