perf stat: Fix transaction lenght metrics

perf stat: Fix transaction lenght metrics

The transaction length metrics in perf stat -T broke recently.

It would not match the metric correctly and always print K/sec.

This was caused by a incorrect update of the cycles_in_tx statistics.

Update the correct variable.

Also the check for zero division was reversed, which resulted in K/sec
being printed for no transactions. Fix this also up.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lkml.kernel.org/r/1438039491-22091-1-git-send-email-andi@firstfloor.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>