First, the CMCI entry index is APIC_LVT_MAX, so it was excluded
unconditionall [1].
Second, the number of entries is reported by the version register, and
we must not access past the last reported entry.
Reported by: olivier [1]
Fixes: 11f954b021a1aadde1d03d40ed5d6b529e14da98
x86/local_apic.c: add lapic_maxlvt() helper
that calculates the max index of the present LVT entry from the value of
the LAPIC version register.