ipmi: refer to table as "SPMI", not "ACPI"

This discovery method uses the SPMI table, not the ACPI namespace.  In
the future, we will look in the namespace, so let's refer to the table
as "SPMI" and save "ACPI" for the namespace.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>