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 <[e-mail]>
Tested-by: Chen-Yu Tsai <[e-mail]>
Acked-by: Tomasz Figa <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

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

···
 
 	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);
···
 		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)) {