usb: add HAS_IOMEM dependency to USB_OHCI_HCD

drivers/built-in.o: In function `ohci_platform_probe':
/home/vegard/linux/drivers/usb/host/ohci-platform.c:246: undefined reference to `devm_ioremap_resource'

Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>