perf script: Fix incorrect python db-export error message

perf script: Fix incorrect python db-export error message

Fix the error message printed when attempting and failing to create the
call path root incorrectly references the call return process.

This change fixes the message to properly reference the failure to
create the call path root.

Signed-off-by: Chris Phlipot <cphlipot0@gmail.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1462612620-25008-2-git-send-email-cphlipot0@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>