media: videobuf2: always set buffer vb2 pointer

We need to always link allocated vb2_dc_buf back to vb2_buffer because
we dereference vb2 in prepare() and finish() callbacks.

Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Acked-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/common/videobuf2/videobuf2-dma-contig.c

@@ -600,6 +600,7 @@ static void *vb2_dc_get_userptr(struct vb2_buffer *vb, struct device *dev,
 
 	buf->dev = dev;
 	buf->dma_dir = vb->vb2_queue->dma_dir;
+	buf->vb = vb;
 
 	offset = lower_32_bits(offset_in_page(vaddr));
 	vec = vb2_create_framevec(vaddr, size);
@@ -788,6 +789,8 @@ static void *vb2_dc_attach_dmabuf(struct vb2_buffer *vb, struct device *dev,
 		return ERR_PTR(-ENOMEM);
 
 	buf->dev = dev;
+	buf->vb = vb;
+
 	/* create attachment for the dmabuf with the user device */
 	dba = dma_buf_attach(dbuf, buf->dev);
 	if (IS_ERR(dba)) {