dma: jz4740: Null pointer dereference

[Stefan Agner <stefan@xxxxxxxx>]

Hi Lars,

While looking through different DMA drivers, just stumbled upon this
inside jz4740_dma_chan_irq:

if (chan->next_sg == chan->desc->num_sgs) {
	chan->desc = NULL;
	vchan_cookie_complete(&chan->desc->vdesc);
                                         ^ null pointer dereference
}

I'm not sure what the correct fix is, hence I thought I report it to you
as author of the driver.

--
Stefan