perf stat: Move the shadow stats scale computation in perf_stat__update_shadow_stats

perf stat: Move the shadow stats scale computation in perf_stat__update_shadow_stats

Move the shadow stats scale computation to the
perf_stat__update_shadow_stats() function, so it's centralized and we
don't forget to do it. It also saves few lines of code.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Changbin Du <changbin.du@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-htg7mmyxv6pcrf57qyo6msid@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>