serial: 8250_bcm7271: fix leak in brcmuart_probe

Smatch reports:
drivers/tty/serial/8250/8250_bcm7271.c:1120 brcmuart_probe() warn:
'baud_mux_clk' from clk_prepare_enable() not released on lines: 1032.

The issue is fixed by using a managed clock.

Fixes: 41a4694 ("serial: 8250: Add new 8250-core based Broadcom STB driver")
Reported-by: XuDong Liu <m202071377@hust.edu.cn>
Link: https://lore.kernel.org/lkml/20230424125100.4783-1-m202071377@hust.edu.cn/
Signed-off-by: Doug Berger <opendmb@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20230427181916.2983697-3-opendmb@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Doug Berger

drivers/tty/serial/8250/8250_bcm7271.c

@@ -1012,7 +1012,7 @@ static int brcmuart_probe(struct platform_device *pdev)
 	of_property_read_u32(np, "clock-frequency", &clk_rate);
 
 	/* See if a Baud clock has been specified */
-	baud_mux_clk = of_clk_get_by_name(np, "sw_baud");
+	baud_mux_clk = devm_clk_get(dev, "sw_baud");
 	if (IS_ERR(baud_mux_clk)) {
 		if (PTR_ERR(baud_mux_clk) == -EPROBE_DEFER) {
 			ret = -EPROBE_DEFER;