perf top: Fix refreshing hierarchy entries on TUI

Markus reported that 'perf top --hierarchy' cannot scroll down after
refresh.  This was because the number of entries are not updated when
hierarchy is enabled.

Unlike normal report view, hierarchy mode needs to keep its own entry
count since it can have non-leaf entries which can expand/collapse.

Reported-and-Tested-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Fixes: f5b763fe

 ("perf hists browser: Count number of hierarchy entries")
Link: http://lkml.kernel.org/r/20161007050412.3000-1-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>