drm: omapdrm: Fix plane state free in plane reset handler

The plane reset handler frees the plane state and allocates a new
default state, but when doing so attempt to free the plane state using
the base plane state pointer instead of casting it to the
driver-specific state object that has been allocated. Fix it by using
the omap_plane_atomic_destroy_state() function to destroy the plane
state instead of duplicating the code.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
[tomi.valkeinen@ti.com: move of the func into separate patch]
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/omap_plane.c

@@ -248,11 +248,10 @@ static void omap_plane_reset(struct drm_plane *plane)
 	struct omap_plane *omap_plane = to_omap_plane(plane);
 	struct omap_plane_state *omap_state;
 
-	if (plane->state && plane->state->fb)
-		drm_framebuffer_unreference(plane->state->fb);
-
-	kfree(plane->state);
+	if (plane->state) {
+		omap_plane_atomic_destroy_state(plane, plane->state);
 		plane->state = NULL;
+	}
 
 	omap_state = kzalloc(sizeof(*omap_state), GFP_KERNEL);
 	if (omap_state == NULL)