x86, UV: Fix smp_processor_id() use in a preemptable region

Fix a call by tunables_write() to smp_processor_id() within a
preemptable region.

Call get_cpu()/put_cpu() around the region where the returned
cpu number is actually used, which makes it non-preemptable.

A DEBUG_PREEMPT warning is prevented.

UV does not support cpu hotplug yet, but this is a step toward
that ability as well.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Link: http://lkml.kernel.org/r/20110621122242.086384966@sgi.com


Signed-off-by: Ingo Molnar <mingo@elte.hu>