perf intel-pt: Factor out intel_pt_update_sample_time

To eliminate some duplication and make the code more understandable,
factor out intel_pt_update_sample_time.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Link: http://lkml.kernel.org/r/20190520113728.14389-5-adrian.hunter@intel.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>