MIPS: Octeon: Fix fixup_irqs for HOTPLUG_CPU

MIPS: Octeon: Fix fixup_irqs for HOTPLUG_CPU

The original version went behind the back of everything, leaving
things in an inconsistent state.

Now we use the irq_set_affinity() to do the work for us.  This has the
advantage that the IRQ core's view of the affinity stays consistent.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
To: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/1486/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>