PEL: Update process_registry.py for python3

The 2to3 program found the places to change, but I didn't use its
suggestions as this is a cleaner way to do it.

Note that this doesn't run during a bitbake or SDK build, but it does
run during CI.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I0c62a832b3249f7dcf4dc67fd0e56ad76367b10a
diff --git a/extensions/openpower-pels/registry/tools/process_registry.py b/extensions/openpower-pels/registry/tools/process_registry.py
index 09ad3e0..24026c3 100755
--- a/extensions/openpower-pels/registry/tools/process_registry.py
+++ b/extensions/openpower-pels/registry/tools/process_registry.py
@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 import argparse
 import json
@@ -20,12 +20,12 @@
     registry_json: The message registry JSON
     """
 
-    names = {}
+    names = []
     for entry in registry_json['PELs']:
-        if entry['Name'] in names.keys():
+        if entry['Name'] in names:
             sys.exit("Found multiple uses of error {}".format(entry['Name']))
         else:
-            names[entry['Name']] = {}
+            names.append(entry['Name'])
 
 
 def check_duplicate_reason_codes(registry_json):
@@ -36,13 +36,13 @@
     registry_json: The message registry JSON
     """
 
-    reasonCodes = {}
+    reasonCodes = []
     for entry in registry_json['PELs']:
-        if entry['SRC']['ReasonCode'] in reasonCodes.keys():
+        if entry['SRC']['ReasonCode'] in reasonCodes:
             sys.exit("Found duplicate SRC reason code {}".format(
                 entry['SRC']['ReasonCode']))
         else:
-            reasonCodes[entry['SRC']['ReasonCode']] = {}
+            reasonCodes.append(entry['SRC']['ReasonCode'])
 
 
 def check_component_id(registry_json):