drm: drm_color_mgmt.h needs struct drm_crtc declaration

Signed-off-by: NJyri Sarha <jsarha@ti.com>
Reviewed-by: NLaurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/69c913b3ae3fc7235c059e08f58fb0a172d98cf8.1492768073.git.jsarha@ti.com

include/drm/drm_color_mgmt.h

@@ -25,6 +25,8 @@
 
 #include <linux/ctype.h>
 
+struct drm_crtc;
+
 uint32_t drm_color_lut_extract(uint32_t user_input, uint32_t bit_precision);
 
 void drm_crtc_enable_color_mgmt(struct drm_crtc *crtc,