dmaengine: fix balance of privatecnt

dma_release_channel() decrements privatecnt counter and almost all dma_get*
function increments it with the exception of dma_get_slave_channel().
In most cases this does not cause issue since normally the channel is not
requested and released, but if a driver requests DMA channel via
dma_get_slave_channel() and releases the channel the privatecnt will be
unbalanced and this will prevent for example getting channel for memcpy.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/dmaengine.c

@@ -554,10 +554,18 @@ struct dma_chan *dma_get_slave_channel(struct dma_chan *chan)
 	mutex_lock(&dma_list_mutex);
 
 	if (chan->client_count == 0) {
+		struct dma_device *device = chan->device;
+
+		dma_cap_set(DMA_PRIVATE, device->cap_mask);
+		device->privatecnt++;
 		err = dma_chan_get(chan);
-		if (err)
+		if (err) {
 			pr_debug("%s: failed to get %s: (%d)\n",
 				__func__, dma_chan_name(chan), err);
+			chan = NULL;
+			if (--device->privatecnt == 0)
+				dma_cap_clear(DMA_PRIVATE, device->cap_mask);
+		}
 	} else
 		chan = NULL;