drm/atomic: Constify drm_atomic_crtc_needs_modeset()

drm_atomic_crtc_needs_modeset() doesn't change the passed in
crtc state, so pass it as const.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1480009622-28127-1-git-send-email-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>

include/drm/drm_atomic.h

@@ -418,7 +418,7 @@ int drm_atomic_debugfs_cleanup(struct drm_minor *minor);
  * should clear mode_changed during its ->atomic_check.
  */
 static inline bool
-drm_atomic_crtc_needs_modeset(struct drm_crtc_state *state)
+drm_atomic_crtc_needs_modeset(const struct drm_crtc_state *state)
 {
 	return state->mode_changed || state->active_changed ||
 	       state->connectors_changed;