powerpc: Mask smp_processor_id() false positive

The rtas_event_scan() function uses smp_processor_id() to select a
starting point in cpu_online_mask, and does so under the protection
of get_online_cpus().  This might not select the current processor
in any case, so switch to raw_smp_processor_id().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>