perf scripts python: export-to-sqlite.py: Fix use of parent_id in calls_view

Fix following error using calls_view:

 Query failed: ambiguous column name: parent_id Unable to execute statement
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Fixes: 8ce9a725 ("perf scripts python: export-to-sqlite.py: Export calls parent_id")
Link: http://lkml.kernel.org/r/20190409062557.26138-1-adrian.hunter@intel.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/python/export-to-sqlite.py

@@ -331,7 +331,7 @@ if perf_db_export_calls:
 			'return_id,'
 			'CASE WHEN flags=0 THEN \'\' WHEN flags=1 THEN \'no call\' WHEN flags=2 THEN \'no return\' WHEN flags=3 THEN \'no call/return\' WHEN flags=6 THEN \'jump\' ELSE flags END AS flags,'
 			'parent_call_path_id,'
-			'parent_id'
+			'calls.parent_id'
 		' FROM calls INNER JOIN call_paths ON call_paths.id = call_path_id')
 
 do_query(query, 'CREATE VIEW samples_view AS '