serial: 8250_pci: Check mapping in pci_ni8430_init

Check the return value of ioremap_nocache to make sure we got a
valid mapping.
Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_pci.c

@@ -757,6 +757,8 @@ pci_ni8430_setup(struct serial_private *priv,
 	offset += idx * board->uart_offset;
 
 	p = pci_ioremap_bar(dev, bar);
+	if (!p)
+		return -ENOMEM;
 
 	/* enable the transceiver */
 	writeb(readb(p + offset + NI8430_PORTCON) | NI8430_PORTCON_TXVR_ENABLE,