perf scripts python: Fix query in call-graph-from-postgresql.py

Add a missing space which seemed not to affect PostgreSQL but upsets
SQLite.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Link: http://lkml.kernel.org/r/1501749090-20357-3-git-send-email-adrian.hunter@intel.com


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