drm/i915: make drm_crtc_helper_funcs const data

Because they can be.
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -11034,7 +11034,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 	return ret;
 }
 
-static struct drm_crtc_helper_funcs intel_helper_funcs = {
+static const struct drm_crtc_helper_funcs intel_helper_funcs = {
 	.mode_set_base_atomic = intel_pipe_set_base_atomic,
 	.load_lut = intel_crtc_load_lut,
 	.atomic_begin = intel_begin_crtc_commit,