perf intel-pt: Improve sample timestamp

perf intel-pt: Improve sample timestamp

The decoder uses its current timestamp in samples. Usually that is a
timestamp that has already passed, but in some cases it is a timestamp
for a branch that the decoder is walking towards, and consequently
hasn't reached. Improve that situation by using the pkt_state to
determine when to use the current or previous timestamp.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1495786658-18063-3-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>