drm/armada: Use drm_plane_helper_destroy()

Replace the driver's own function with drm_plane_helper_destroy(). No
functional changes.

Signed-off-by: Thomas Zimmermann <[e-mail]>
Reviewed-by: Sam Ravnborg <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/armada/armada_overlay.c

···
 #include <drm/drm_atomic_helper.h>
 #include <drm/drm_atomic_uapi.h>
 #include <drm/drm_fourcc.h>
+#include <drm/drm_plane_helper.h>
 
 #include "armada_crtc.h"
 #include "armada_drm.h"
···
 	return ret;
 }
 
-static void armada_ovl_plane_destroy(struct drm_plane *plane)
-{
-	drm_plane_cleanup(plane);
-	kfree(plane);
-}
-
 static void armada_overlay_reset(struct drm_plane *plane)
 {
 	struct armada_overlay_state *state;
···
 static const struct drm_plane_funcs armada_ovl_plane_funcs = {
 	.update_plane	= armada_overlay_plane_update,
 	.disable_plane	= drm_atomic_helper_disable_plane,
-	.destroy	= armada_ovl_plane_destroy,
+	.destroy	= drm_plane_helper_destroy,
 	.reset		= armada_overlay_reset,
 	.atomic_duplicate_state = armada_overlay_duplicate_state,
 	.atomic_destroy_state = drm_atomic_helper_plane_destroy_state,