media: uvcvideo: Refactor iterators

Avoid using the iterators after the list_for_each() constructs.
This patch should be a NOP, but makes cocci, happier:

drivers/media/usb/uvc/uvc_ctrl.c:1861:44-50: ERROR: invalid reference to the index variable of the iterator on line 1850
drivers/media/usb/uvc/uvc_ctrl.c:2195:17-23: ERROR: invalid reference to the index variable of the iterator on line 2179

Reviewed-by: Sergey Senozhatsky <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Ricardo Ribalda <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/usb/uvc/uvc_ctrl.c

···
 	list_for_each_entry(entity, &chain->entities, chain) {
 		ret = uvc_ctrl_commit_entity(chain->dev, entity, rollback,
 					     &err_ctrl);
-		if (ret < 0)
+		if (ret < 0) {
+			if (ctrls)
+				ctrls->error_idx =
+					uvc_ctrl_find_ctrl_idx(entity, ctrls,
+							       err_ctrl);
 			goto done;
+		}
 	}
 
 	if (!rollback)
 		uvc_ctrl_send_events(handle, ctrls->controls, ctrls->count);
 done:
-	if (ret < 0 && ctrls)
-		ctrls->error_idx = uvc_ctrl_find_ctrl_idx(entity, ctrls,
-							  err_ctrl);
 	mutex_unlock(&chain->ctrl_mutex);
 	return ret;
 }
···
 int uvc_xu_ctrl_query(struct uvc_video_chain *chain,
 	struct uvc_xu_control_query *xqry)
 {
-	struct uvc_entity *entity;
+	struct uvc_entity *entity, *iter;
 	struct uvc_control *ctrl;
 	unsigned int i;
 	bool found;
···
 	int ret;
 
 	/* Find the extension unit. */
-	found = false;
-	list_for_each_entry(entity, &chain->entities, chain) {
-		if (UVC_ENTITY_TYPE(entity) == UVC_VC_EXTENSION_UNIT &&
-		    entity->id == xqry->unit) {
-			found = true;
+	entity = NULL;
+	list_for_each_entry(iter, &chain->entities, chain) {
+		if (UVC_ENTITY_TYPE(iter) == UVC_VC_EXTENSION_UNIT &&
+		    iter->id == xqry->unit) {
+			entity = iter;
 			break;
 		}
 	}
 
-	if (!found) {
+	if (!entity) {
 		uvc_dbg(chain->dev, CONTROL, "Extension unit %u not found\n",
 			xqry->unit);
 		return -ENOENT;