backlight/corgi-lcd: Include <linux/backlight.h>

Resolves the proxy include via <linux/fb.h>, which does not require the
backlight header.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Lee Jones <lee@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240219093941.3684-2-tzimmermann@suse.de

drivers/video/backlight/corgi_lcd.c

@@ -11,6 +11,7 @@
  *	by Eric Miao <eric.miao@marvell.com>
  */
 
+#include <linux/backlight.h>
 #include <linux/module.h>
 #include <linux/kernel.h>
 #include <linux/init.h>