dmaengine: at_hdmac: no need set ACK in new descriptor

Following descriptor flow in at_hdmac driver, descriptor comming from
atc_desc_get() as already DMA_CTRL_ACK flag set. No need to set it again.
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/dma/at_hdmac.c

@@ -583,7 +583,6 @@ atc_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
 		desc->lli.ctrlb = ctrlb;
 
 		desc->txd.cookie = 0;
-		async_tx_ack(&desc->txd);
 
 		if (!first) {
 			first = desc;