drm: Constify drm_mode_config_funcs pointer

The DRM mode config functions structure declared by drivers and pointed
to by the drm_mode_config funcs field is never modified. Make it a const
pointer.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Inki Dae <inki.dae@samsung.com>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: Thomas Hellstrom <thellstrom@vmware.com>
Cc: Rob Clark <rob.clark@linaro.org>
Reviwed-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
index 3ecee19..b88b28f 100644
--- a/include/drm/drm_crtc.h
+++ b/include/drm/drm_crtc.h
@@ -767,7 +767,7 @@
 
 	int min_width, min_height;
 	int max_width, max_height;
-	struct drm_mode_config_funcs *funcs;
+	const struct drm_mode_config_funcs *funcs;
 	resource_size_t fb_base;
 
 	/* output poll support */