perf top: Don't update total_period on process_sample

It will be recalculated at __hists__output_resort, to take into account
filters possibly applied by the TUI, etc.

Since we do the percent math only for those entries that will appear on
the TUI instead of for _all_ the entries at decay time, updating it for
each sample makes the entries seem to decay faster when using the
navigation keys (since the screen will be refreshed), as we're not
coalescing the entries that are being batched to be merged at next
resort/decay time, but considering their periods.

Bug introduced in 743eb86.

Reported-by: Ingo Molnar <mingo@elte.hu>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-k0d0rq9a8nqtkqohov8cir72@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>