Fix adding emails on registration

Synapse was not adding email addresses to accounts registered with an email address, due to too many different variables called 'result'. Rename both of them. Also remove the defer.returnValue() with no params because that's not a thing.

synapse/rest/client/v2_alpha/register.py

@@ -196,12 +196,12 @@ class RegisterRestServlet(RestServlet):
                 [LoginType.EMAIL_IDENTITY]
             ]
 
-        authed, result, params, session_id = yield self.auth_handler.check_auth(
+        authed, auth_result, params, session_id = yield self.auth_handler.check_auth(
             flows, body, self.hs.get_ip_from_request(request)
         )
 
         if not authed:
-            defer.returnValue((401, result))
+            defer.returnValue((401, auth_result))
             return
 
         if registered_user_id is not None:
@@ -236,18 +236,18 @@ class RegisterRestServlet(RestServlet):
 
             add_email = True
 
-        result = yield self._create_registration_details(
+        return_dict = yield self._create_registration_details(
             registered_user_id, params
         )
 
-        if add_email and result and LoginType.EMAIL_IDENTITY in result:
-            threepid = result[LoginType.EMAIL_IDENTITY]
+        if add_email and auth_result and LoginType.EMAIL_IDENTITY in auth_result:
+            threepid = auth_result[LoginType.EMAIL_IDENTITY]
             yield self._register_email_threepid(
-                registered_user_id, threepid, result["access_token"],
+                registered_user_id, threepid, return_dict["access_token"],
                 params.get("bind_email")
             )
 
-        defer.returnValue((200, result))
+        defer.returnValue((200, return_dict))
 
     def on_OPTIONS(self, _):
         return 200, {}
@@ -356,8 +356,6 @@ class RegisterRestServlet(RestServlet):
         else:
             logger.info("bind_email not specified: not binding email")
 
-        defer.returnValue()
-
     @defer.inlineCallbacks
     def _create_registration_details(self, user_id, params):
         """Complete registration of newly-registered user