tty: serial: amba-pl011: Use dma_request_chan() directly for channel request

dma_request_slave_channel_reason() is:
#define dma_request_slave_channel_reason(dev, name) \
	dma_request_chan(dev, name)
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20191113094618.1725-2-peter.ujfalusi@ti.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -414,7 +414,7 @@ static void pl011_dma_probe(struct uart_amba_port *uap)
 	dma_cap_mask_t mask;
 
 	uap->dma_probed = true;
-	chan = dma_request_slave_channel_reason(dev, "tx");
+	chan = dma_request_chan(dev, "tx");
 	if (IS_ERR(chan)) {
 		if (PTR_ERR(chan) == -EPROBE_DEFER) {
 			uap->dma_probed = false;