[media] V4L: sh_mobile_ceu_camera: fix Oops when USERPTR mapping fails

If vb2_dma_contig_get_userptr() fails on a videobuffer, driver's
.buf_init() method will not be called and the list will not be
initialised. Trying to remove an uninitialised element from a list leads
to a NULL-dereference.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Tested-by: Bastian Hecht <hechtb@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/sh_mobile_ceu_camera.c

@@ -422,8 +422,12 @@ static void sh_mobile_ceu_videobuf_release(struct vb2_buffer *vb)
 		pcdev->active = NULL;
 	}
 
-	/* Doesn't hurt also if the list is empty */
-	list_del_init(&buf->queue);
+	/*
+	 * Doesn't hurt also if the list is empty, but it hurts, if queuing the
+	 * buffer failed, and .buf_init() hasn't been called
+	 */
+	if (buf->queue.next)
+		list_del_init(&buf->queue);
 
 	spin_unlock_irq(&pcdev->lock);
 }