perf annotate: Do not overwrite sample->period

In fixing the --show-total-period option it was noticed that the value
of sample->period was being overwritten, fix it.

Signed-off-by: Taeung Song <treeze.taeung@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Fixes: fd36f3dd

 ("perf hist: Pass struct sample to __hists__add_entry()")
Link: http://lkml.kernel.org/r/1500500215-16646-1-git-send-email-treeze.taeung@gmail.com
[ split from a larger patch, added the Fixes tag ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>