serial: amba-pl011: convert not to use dma_request_slave_channel()

dma_request_slave_channel() is deprecated. dma_request_chan() should
be used directly instead.

Switch to the preferred function and update the error handling accordingly.
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/6f76e22f77d776d6c1f176d56e7ee341314d8554.1700405529.git.christophe.jaillet@wanadoo.frSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -444,9 +444,9 @@ static void pl011_dma_probe(struct uart_amba_port *uap)
 		 dma_chan_name(uap->dmatx.chan));
 
 	/* Optionally make use of an RX channel as well */
-	chan = dma_request_slave_channel(dev, "rx");
+	chan = dma_request_chan(dev, "rx");
 
-	if (!chan && plat && plat->dma_rx_param) {
+	if (IS_ERR(chan) && plat && plat->dma_rx_param) {
 		chan = dma_request_channel(mask, plat->dma_filter, plat->dma_rx_param);
 
 		if (!chan) {
@@ -455,7 +455,7 @@ static void pl011_dma_probe(struct uart_amba_port *uap)
 		}
 	}
 
-	if (chan) {
+	if (!IS_ERR(chan)) {
 		struct dma_slave_config rx_conf = {
 			.src_addr = uap->port.mapbase +
 				pl011_reg_to_offset(uap, REG_DR),