drm/atomic: Add missing () to function ref in kerneldoc

Pure drive-by while reading code&docs.
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181012073441.21774-1-daniel.vetter@ffwll.ch

include/drm/drm_atomic.h

@@ -139,9 +139,9 @@ struct drm_crtc_commit {
 	/**
 	 * @abort_completion:
 	 *
-	 * A flag that's set after drm_atomic_helper_setup_commit takes a second
-	 * reference for the completion of $drm_crtc_state.event. It's used by
-	 * the free code to remove the second reference if commit fails.
+	 * A flag that's set after drm_atomic_helper_setup_commit() takes a
+	 * second reference for the completion of $drm_crtc_state.event. It's
+	 * used by the free code to remove the second reference if commit fails.
 	 */
 	bool abort_completion;
 };