drm/atmel: Fixup drm_connector_/unplug/unregister/_all

Accidentally fell through the cracks in

commit 6c87e5c3ec6db052f3744804a517b6fb003906e1
Author: Alexey Brodkin <Alexey.Brodkin@synopsys.com>
Date:   Wed Mar 23 11:42:54 2016 +0300

    drm: Rename drm_connector_unplug_all() to drm_connector_unregister_all()

despite that Boris acked that patch.

Cc: Boris Brezillon <boris.brezillon@free-electrons.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c

@@ -615,7 +615,7 @@ err:
 static void atmel_hlcdc_dc_connector_unplug_all(struct drm_device *dev)
 {
 	mutex_lock(&dev->mode_config.mutex);
-	drm_connector_unplug_all(dev);
+	drm_connector_unregister_all(dev);
 	mutex_unlock(&dev->mode_config.mutex);
 }