net: openvswitch: use this_cpu_ptr per-cpu helper

just use more faster this_cpu_ptr instead of per_cpu_ptr(p, smp_processor_id());

Signed-off-by: Shan Wei <davidshan@tencent.com>
Reviewed-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>