mfd: Change rdc321x resources flags to IORESOURCE_IO

The rdc321x southbridge PCI device has no MEM PCI resources that we could
pass to mfd_add_devices. Since 33254dd5, mfd_add_device checks for the
mem_base argument that we set to NULL. Changing the resources passed to
our MFD cells from IORESOURCE_MEM to IORESOURCE_IO fixes that. Since we use
those resources as offsets to the PCI configuration space base address of
the southbridge device this is also more adequate.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>