drm/atomic: Add missing drm_crtc_internal.h include

Some of the functions implemented are flagged as not having a prototype
defined when building with W=1. Include the header to avoid these build
warnings.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1461849596-12819-1-git-send-email-thierry.reding@gmail.com

drivers/gpu/drm/drm_atomic.c

@@ -31,6 +31,8 @@
 #include <drm/drm_mode.h>
 #include <drm/drm_plane_helper.h>
 
+#include "drm_crtc_internal.h"
+
 /**
  * drm_atomic_state_default_release -
  * release memory initialized by drm_atomic_state_init