drm/panel: s6e8aa0: Use static inline for upcasting

Use a static inline function for upcasting a struct drm_panel to the
driver-specific structure. The advantage over using a macro is that it
gives us additional type checking.
Acked-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/panel/panel-s6e8aa0.c

@@ -120,7 +120,10 @@ struct s6e8aa0 {
 	int error;
 };
 
-#define panel_to_s6e8aa0(p) container_of(p, struct s6e8aa0, panel)
+static inline struct s6e8aa0 *panel_to_s6e8aa0(struct drm_panel *panel)
+{
+	return container_of(panel, struct s6e8aa0, panel);
+}
 
 static int s6e8aa0_clear_error(struct s6e8aa0 *ctx)
 {