perf scripts intel-pt-events.py: Fix IPC output for Python 2

perf scripts intel-pt-events.py: Fix IPC output for Python 2

Integers are not converted to floats during division in Python 2 which
results in incorrect IPC values. Fix by switching to new division
behavior.

Fixes: a483e64c0b62e93a ("perf scripting python: intel-pt-events.py: Add --insn-trace and --src-trace")
Signed-off-by: Roman Lozko <lozko.roma@gmail.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20230310150445.2925841-1-lozko.roma@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>