x86: remove BUG_ON() from QUIRK_IOAPIC_*_REGSEL handler

x86: remove BUG_ON() from QUIRK_IOAPIC_*_REGSEL handler

Since (non-pvops, 32-bit only up to 2.6.27) Linux would report "BAD"
unconditionally on all SiS chipset versions (it only looks for a PCI
device at 0000:00:00.0 with SiS as the vendor), we must not crash if
the report on a 64-bit hypervisor doesn't match the #define (which is
zero).

While we could honor the quirk indication even on 64-bit, it doesn't
seem worthwhile, as there's no evidence that newer SiS chipsets
(supporting 64-bit CPUs) are actually affected.

This should also address bug 1687 (mis-reported, however, afaict).

Signed-off-by: Jan Beulich <jbeulich@novell.com>