serial: 8250_bcm7271: Fix return value check in brcmuart_probe()

In case of error, the function devm_ioremap() returns NULL
pointer not ERR_PTR(). The IS_ERR() test in the return value
check should be replaced with NULL test.

Fixes: 41a46948 ("serial: 8250: Add new 8250-core based Broadcom STB driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Reviewed-by: Al Cooper <alcooperx@gmail.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210329140659.1832950-1-weiyongjun1@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

@@ -974,8 +974,8 @@ static int brcmuart_probe(struct platform_device *pdev)
 			break;
 		priv->regs[x] =	devm_ioremap(dev, regs->start,
 					     resource_size(regs));
-		if (IS_ERR(priv->regs[x]))
-			return PTR_ERR(priv->regs[x]);
+		if (!priv->regs[x])
+			return -ENOMEM;
 		if (x == REGS_8250) {
 			mapbase = regs->start;
 			membase = priv->regs[x];