Sometimes the PCIe card indicates that it has a sprom somewhere and we
are able to read the memory region, but it is empty and not valid. In
these cases we should try to use the fallback sprom as a last chance.
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@33601 3c298f89-4303-0410-b956-a3cf2f4a3e73
