drm/nouveau: Include <linux/backlight.h>

Resolves the proxy include via <linux/fb.h>, which does not require the
backlight header.

v3:
	* fix grammar in commit message
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Acked-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240219093941.3684-3-tzimmermann@suse.de

drivers/gpu/drm/nouveau/dispnv50/disp.c

@@ -28,6 +28,7 @@
 #include "wndw.h"
 #include "handles.h"
 
+#include <linux/backlight.h>
 #include <linux/dma-mapping.h>
 #include <linux/hdmi.h>
 #include <linux/component.h>