serial: 8250_bcm2835aux: Restore clock error handling

The commit fcc446c ("serial: 8250_bcm2835aux: Add ACPI support")
dropped the error handling for clock acquiring. But even an optional
clock needs this.

Fixes: fcc446c ("serial: 8250_bcm2835aux: Add ACPI support")
Cc: stable <stable@kernel.org>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Reviewed-by: Florian Fainelli <florian.fainelli@broadcom.com>
Link: https://lore.kernel.org/r/20231220114334.4712-1-wahrenst@gmx.net
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_bcm2835aux.c

@@ -119,6 +119,8 @@ static int bcm2835aux_serial_probe(struct platform_device *pdev)
 
 	/* get the clock - this also enables the HW */
 	data->clk = devm_clk_get_optional(&pdev->dev, NULL);
+	if (IS_ERR(data->clk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(data->clk), "could not get clk\n");
 
 	/* get the interrupt */
 	ret = platform_get_irq(pdev, 0);