8250_lpss: check null return when calling pci_ioremap_bar

8250_lpss: check null return when calling pci_ioremap_bar

pci_ioremap_bar may return null. This is eventually de-referenced at
drivers/dma/dw/core.c:1154 and drivers/dma/dw/core.c:1168. A null check
is needed to prevent null de-reference. I am adding the check and in
case of failure. Thanks to Andy Shevchenko for the hint on the necessity
of pci_iounmap when exiting.

Signed-off-by: Navid Emamdoost <navid.emamdoost@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20190719174848.24216-1-navid.emamdoost@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>