server: revert commit 7e6556b3ca

With the removal of old tpiu code, commit 7e6556b3ca ("server:
permit the add_service function to return the created service")
http://openocd.zylin.com/5717/ can be reverted.

Fix also the new calls to add_service().

Change-Id: Ib7f2dfc6a9e829239e20313e0f121911085fdc00
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6031
Tested-by: jenkins
Reviewed-by: Adrian M Negreanu <adrian.negreanu@nxp.com>

src/server/telnet_server.c

@@ -694,7 +694,7 @@ int telnet_init(char *banner)
 
 	int ret = add_service("telnet", telnet_port, CONNECTION_LIMIT_UNLIMITED,
 		telnet_new_connection, telnet_input, telnet_connection_closed,
-		telnet_service, NULL);
+		telnet_service);
 
 	if (ret != ERROR_OK) {
 		free(telnet_service);