pch_dma: Use GFP_ATOMIC because called from interrupt context

pdc_desc_get() is called from pd_prep_slave_sg, and the function is
called from interrupt context(e.g. Uart driver "pch_uart.c").
In fact, I saw kernel error message.
So, GFP_ATOMIC must be used not GFP_NOIO.

Signed-off-by: Tomoya MORINAGA <tomoya.rohm@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

Author: Tomoya MORINAGA

drivers/dma/pch_dma.c

@@ -476,7 +476,7 @@ static struct pch_dma_desc *pdc_desc_get(struct pch_dma_chan *pd_chan)
 	dev_dbg(chan2dev(&pd_chan->chan), "scanned %d descriptors\n", i);
 
 	if (!ret) {
-		ret = pdc_alloc_desc(&pd_chan->chan, GFP_NOIO);
+		ret = pdc_alloc_desc(&pd_chan->chan, GFP_ATOMIC);
 		if (ret) {
 			spin_lock(&pd_chan->lock);
 			pd_chan->descs_allocated++;