powerpc, irq: Use access helper irq_data_get_affinity_mask()

Use access helper irq_data_get_affinity_mask() so we can move the
affinity mask to irq_common_data.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1433145945-789-25-git-send-email-jiang.liu@linux.intel.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>