x86: apic - calibrate_APIC_clock remove redundant irq-enable-disable

Impact: cleanup

lapic_timer_setup is self-protected with local_irq_save/restore
no need to use them in caller and levt is the per-cpu variable so
no concurrent access from another cpu.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Acked-by: "Maciej W. Rozycki" <macro@linux-mips.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>