drm/atomic: Use new iterator macros in drm_atomic_helper_wait_for_flip_done, again.

for_each_obj_in_state is about to be removed, so use the correct new
iterator macro.

I renamed the variable to 'unused', but forgot to convert
drm_atomic_helper_wait_for_flip_done to the new iterator macro,
so make it work this time.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Link: https://patchwork.freedesktop.org/patch/msgid/20170719143920.25685-2-maarten.lankhorst@linux.intel.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_atomic_helper.c

@@ -1270,7 +1270,7 @@ void drm_atomic_helper_wait_for_flip_done(struct drm_device *dev,
 	struct drm_crtc *crtc;
 	int i;
 
-	for_each_crtc_in_state(old_state, crtc, unused, i) {
+	for_each_new_crtc_in_state(old_state, crtc, unused, i) {
 		struct drm_crtc_commit *commit = old_state->crtcs[i].commit;
 		int ret;