perf intel-pt: Fix divide by zero when TSC is not available

perf intel-pt: Fix divide by zero when TSC is not available

commit 076333870c2f5bdd9b6d31e7ca1909cf0c84cbfa upstream.

When TSC is not available, "timeless" decoding is used but a divide by
zero occurs if perf_time_to_tsc() is called.

Ensure the divisor is not zero.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: stable@vger.kernel.org # v4.9+
Link: https://lkml.kernel.org/n/tip-1i4j0wqoc8vlbkcizqqxpsf4@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>