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>
diff --git a/drivers/tty/serial/8250/8250_pci.c b/drivers/tty/serial/8250/8250_pci.c
index 50f7570..003679f 100644
--- a/drivers/tty/serial/8250/8250_pci.c
+++ b/drivers/tty/serial/8250/8250_pci.c
@@ -757,6 +757,8 @@
 	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,