Fix !CONFIG_SMP warning:

arch/x86/kernel/acpi/processor.c: In function arch_acpi_processor_init_pdc:
arch/x86/kernel/acpi/processor.c:65: warning: unused variable cpu
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>