drm/nouveau/led: explicitly include linux/leds.h

Instead of relying on an accidental, transitive inclusion of linux/leds.h
use it directly.

Also drop the forware definition of struct led_classdev that is now
provided by linux/leds.h.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230215-power_supply-leds-nouveau-v1-1-ea93bfa0ba7e@weissschuh.net

drivers/gpu/drm/nouveau/nouveau_led.h

@@ -27,7 +27,7 @@
 
 #include "nouveau_drv.h"
 
-struct led_classdev;
+#include <linux/leds.h>
 
 struct nouveau_led {
 	struct drm_device *dev;