x86: don't read maxlvt before checking if APIC is mapped

A check for unmapped apic was added before reading maxlvt but the early
read of maxlvt wasn't removed.

Signed-off-by: Chuck Ebbert <cebbert@redhat.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org