Revert "media: remove unused variable that causes a warning"

This reverts commit 12b27ff59a1ecad4b4441bb1a56c0c7a62f71c73.

This fix was rejected by LTS
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 5c19779..f2e43de 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -3222,6 +3222,7 @@
 int vb2_thread_stop(struct vb2_queue *q)
 {
 	struct vb2_threadio_data *threadio = q->threadio;
+	struct vb2_fileio_data *fileio = q->fileio;
 	int err;
 
 	if (threadio == NULL)