serial: liteuart: fix return value check in liteuart_probe()

In case of error, the function devm_platform_get_and_ioremap_resource()
returns ERR_PTR() and never returns NULL. The NULL test in the return
value check should be replaced with IS_ERR().

Fixes: 1da81e55 ("drivers/tty/serial: add LiteUART driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210305034929.3234352-1-weiyongjun1@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/liteuart.c

@@ -270,8 +270,8 @@ static int liteuart_probe(struct platform_device *pdev)
 
 	/* get membase */
 	port->membase = devm_platform_get_and_ioremap_resource(pdev, 0, NULL);
-	if (!port->membase)
-		return -ENXIO;
+	if (IS_ERR(port->membase))
+		return PTR_ERR(port->membase);
 
 	/* values not from device tree */
 	port->dev = &pdev->dev;