serial: amba-pl011: Fix devm_ioremap_resource return value check

Value returned by devm_ioremap_resource() was checked for non-NULL but
devm_ioremap_resource() returns IOMEM_ERR_PTR, not NULL. In case of
error this could lead to dereference of ERR_PTR.
Signed-off-by: Krzysztof Kozlowski <k.kozlowski.k@gmail.com>
Cc: <stable@vger.kernel.org>
Fixes: 3873e2d7 ("drivers: PL011: refactor pl011_probe()")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/amba-pl011.c

@@ -2310,8 +2310,8 @@ static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
 	void __iomem *base;
 
 	base = devm_ioremap_resource(dev, mmiobase);
-	if (!base)
-		return -ENOMEM;
+	if (IS_ERR(base))
+		return PTR_ERR(base);
 
 	index = pl011_probe_dt_alias(index, dev);