x86: make 64 handle sis_apic_bug like the 32 bit

do we have 64bit system with sis chipset?

[ mingo@elte.hu: nope, the problem chipset was 32-bit only.
                 The code symmetry is good nevertheless. ]

Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>