drm/loongson: fix build after debugfs include change

This failed to build here after the header rework.

Fixes: 33d5ae6cacf4 ("drm/print: drop include debugfs.h and include where needed")
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/loongson/lsdc_crtc.c

···
  * Copyright (C) 2023 Loongson Technology Corporation Limited
  */
 
+#include <linux/debugfs.h>
 #include <linux/delay.h>
 
 #include <drm/drm_atomic.h>