media: mediatek: vcodec: fix potential double free

The "lat_buf->private_data" needs to be set to NULL to prevent a
double free.  How this would happen is if vdec_msg_queue_init() failed
twice in a row and on the second time it failed earlier than on the
first time.

The vdec_msg_queue_init() function has a loop which does:
	for (i = 0; i < NUM_BUFFER_COUNT; i++) {

Each iteration initializes one element in the msg_queue->lat_buf[] array
and then the clean up function vdec_msg_queue_deinit() frees each
element of the msg_queue->lat_buf[] array.  This clean up code relies
on the assumption that every element is either initialized or zeroed.
Leaving a freed pointer which is non-zero breaks the assumption.

Fixes: b199fe46 ("media: mtk-vcodec: Add msg queue feature for lat and core architecture")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/platform/mediatek/vcodec/vdec_msg_queue.c

@@ -231,6 +231,7 @@ void vdec_msg_queue_deinit(struct vdec_msg_queue *msg_queue,
 			mtk_vcodec_mem_free(ctx, mem);
 
 		kfree(lat_buf->private_data);
+		lat_buf->private_data = NULL;
 	}
 
 	if (msg_queue->wdma_addr.size)