drm/panel-ili9341: Include <linux/backlight.h>

Include <linux/backlight.h> for devm_of_find_backlight().
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221103151446.2638-10-tzimmermann@suse.de

drivers/gpu/drm/panel/panel-ilitek-ili9341.c

@@ -18,6 +18,7 @@
  * Copyright 2018 David Lechner <david@lechnology.com>
  */
 
+#include <linux/backlight.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>
 #include <linux/gpio/consumer.h>