drm/atmel-hlcdc: Drop custom encoder cleanup func.

drm_encoder_cleanup() finishes with memsetting it to 0, already.
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Archit Taneja <architt@codeaurora.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20170511183128.25085-6-eric@anholt.net

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

@@ -83,14 +83,8 @@ static const struct drm_encoder_helper_funcs atmel_hlcdc_panel_encoder_helper_fu
 	.enable = atmel_hlcdc_rgb_encoder_enable,
 };
 
-static void atmel_hlcdc_rgb_encoder_destroy(struct drm_encoder *encoder)
-{
-	drm_encoder_cleanup(encoder);
-	memset(encoder, 0, sizeof(*encoder));
-}
-
 static const struct drm_encoder_funcs atmel_hlcdc_panel_encoder_funcs = {
-	.destroy = atmel_hlcdc_rgb_encoder_destroy,
+	.destroy = drm_encoder_cleanup,
 };
 
 static int atmel_hlcdc_panel_get_modes(struct drm_connector *connector)