drm/i915: make drm_crtc_helper_funcs const data

Because they can be.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 14709547..abbca0e 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -11034,7 +11034,7 @@
 	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,