x86: apic_64.c - add sanity check for spurious vector definition

Do not check for SPUTIOUS_APIC_VECTOR definition twice.
Check it once - is what we need.

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