perf scripts python: Fix missing call_path_id in export-to-postgresql script

perf scripts python: Fix missing call_path_id in export-to-postgresql script

The export does not work if only branches are exported because of a
missing column in the samples table.  Fix by adding the missing
call_path_id.

Fixes: 3521f3bc9dae ("perf script: Update export-to-postgresql to support callchain export")
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Link: http://lkml.kernel.org/r/1501749090-20357-2-git-send-email-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>