the BIOS bug workaround for the i82443BX chipset's DRAM leadoff timing
parameter is not needed for revisions >= C0, so avoid tweaking that
parameter in that case.
Earlier, this would trigger NMIs on fully memory-populated Compaq
1850R systems, where the BIOS appears to program and require a non-
standard value for this parameter.
Thanks to Chris Ross for the diagnosis and the fix!