monitor/qmp-cmds: rename Error ** parameter to more common errp

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20191205174635.18758-14-vsementsov@virtuozzo.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

monitor/qmp-cmds.c

@@ -109,7 +109,7 @@ void qmp_system_reset(Error **errp)
     qemu_system_reset_request(SHUTDOWN_CAUSE_HOST_QMP_SYSTEM_RESET);
 }
 
-void qmp_system_powerdown(Error **erp)
+void qmp_system_powerdown(Error **errp)
 {
     qemu_system_powerdown_request();
 }