slimbus: qcom-ngd-ctrl: Use dma_request_chan() instead dma_request_slave_channel()

dma_request_slave_channel() is a wrapper on top of dma_request_chan()
eating up the error code.

By using dma_request_chan() directly the driver can support deferred
probing against DMA.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200109103148.5612-3-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/slimbus/qcom-ngd-ctrl.c

@@ -666,10 +666,12 @@ static int qcom_slim_ngd_init_rx_msgq(struct qcom_slim_ngd_ctrl *ctrl)
 	struct device *dev = ctrl->dev;
 	int ret, size;
 
-	ctrl->dma_rx_channel = dma_request_slave_channel(dev, "rx");
-	if (!ctrl->dma_rx_channel) {
-		dev_err(dev, "Failed to request dma channels");
-		return -EINVAL;
+	ctrl->dma_rx_channel = dma_request_chan(dev, "rx");
+	if (IS_ERR(ctrl->dma_rx_channel)) {
+		dev_err(dev, "Failed to request RX dma channel");
+		ret = PTR_ERR(ctrl->dma_rx_channel);
+		ctrl->dma_rx_channel = NULL;
+		return ret;
 	}
 
 	size = QCOM_SLIM_NGD_DESC_NUM * SLIM_MSGQ_BUF_LEN;
@@ -703,10 +705,12 @@ static int qcom_slim_ngd_init_tx_msgq(struct qcom_slim_ngd_ctrl *ctrl)
 	int ret = 0;
 	int size;
 
-	ctrl->dma_tx_channel = dma_request_slave_channel(dev, "tx");
-	if (!ctrl->dma_tx_channel) {
-		dev_err(dev, "Failed to request dma channels");
-		return -EINVAL;
+	ctrl->dma_tx_channel = dma_request_chan(dev, "tx");
+	if (IS_ERR(ctrl->dma_tx_channel)) {
+		dev_err(dev, "Failed to request TX dma channel");
+		ret = PTR_ERR(ctrl->dma_tx_channel);
+		ctrl->dma_tx_channel = NULL;
+		return ret;
 	}
 
 	size = ((QCOM_SLIM_NGD_DESC_NUM + 1) * SLIM_MSGQ_BUF_LEN);