PCI: Don't convert BAR address to resource if dma_addr_t is too small

If dma_addr_t is too small to represent the BAR value,
pcibios_bus_to_resource() will fail, so just remember the BAR size directly
in the resource.  The resource is already marked UNSET, so we know the
address isn't valid anyway.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>