ipmi:dmi: Ignore IPMI SMBIOS entries with a zero base address

Looking at logs from systems all over the place, it looks like tons
of broken systems exist that set the base address to zero.  I can
only guess that is some sort of non-standard idea to mark the
interface as not being present.  It can't be zero, anyway, so just
complain and ignore it.

Signed-off-by: Corey Minyard <cminyard@mvista.com>