powerpc: Use physical cpu id when setting the processor affinity

In the CONFIG_SMP case the irq_choose_cpu() code was returning back
a logical cpu id not the physical id.  We were writing that directly
into the HW register.

We need to be calling get_hard_smp_processor_id() so irq_choose_cpu()
always returns a physical cpu id.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>