drm: Convert all helpers to drm_connector_list_iter

Mostly nothing special (except making sure that really all error paths
and friends call iter_put).

v2: Don't forget the raw connector_list walking in
drm_helper_move_panel_connectors_to_head. That one unfortunately can't
be converted to the iterator helpers, but since it's just some list
splicing best to just wrap the entire thing up in one critical
section.

v3: Bail out after iter_put (Harry).

Cc: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20161215155843.13408-1-daniel.vetter@ffwll.ch
diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
index 191a5f0..8b042a1 100644
--- a/drivers/gpu/drm/drm_plane_helper.c
+++ b/drivers/gpu/drm/drm_plane_helper.c
@@ -75,6 +75,7 @@ static int get_connectors_for_crtc(struct drm_crtc *crtc,
 {
 	struct drm_device *dev = crtc->dev;
 	struct drm_connector *connector;
+	struct drm_connector_list_iter conn_iter;
 	int count = 0;
 
 	/*
@@ -84,7 +85,8 @@ static int get_connectors_for_crtc(struct drm_crtc *crtc,
 	 */
 	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
 
-	drm_for_each_connector(connector, dev) {
+	drm_connector_list_iter_get(dev, &conn_iter);
+	drm_for_each_connector_iter(connector, &conn_iter) {
 		if (connector->encoder && connector->encoder->crtc == crtc) {
 			if (connector_list != NULL && count < num_connectors)
 				*(connector_list++) = connector;
@@ -92,6 +94,7 @@ static int get_connectors_for_crtc(struct drm_crtc *crtc,
 			count++;
 		}
 	}
+	drm_connector_list_iter_put(&conn_iter);
 
 	return count;
 }