dmaengine: pch_dma: remove unused ‘cookie’

In pd_tx_submit(), variable ‘cookie’ is initialized but never used, which
leads to warning with W=1

drivers/dma/pch_dma.c: In function ‘pd_tx_submit’:
drivers/dma/pch_dma.c:420:15: warning: variable ‘cookie’ set but not used [-Wunused-but-set-variable]
  dma_cookie_t cookie;

So remove it.
Signed-off-by: NVinod Koul <vinod.koul@intel.com>

drivers/dma/pch_dma.c

@@ -417,10 +417,8 @@ static dma_cookie_t pd_tx_submit(struct dma_async_tx_descriptor *txd)
 {
 	struct pch_dma_desc *desc = to_pd_desc(txd);
 	struct pch_dma_chan *pd_chan = to_pd_chan(txd->chan);
-	dma_cookie_t cookie;
 
 	spin_lock(&pd_chan->lock);
-	cookie = dma_cookie_assign(txd);
 
 	if (list_empty(&pd_chan->active_list)) {
 		list_add_tail(&desc->desc_node, &pd_chan->active_list);