sh: Use irq_set_affinity instead of homebrewn code

There is no point in having an incomplete copy of irq_set_affinity()
for the hotplug irq migration code.

Use the core function instead.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: sh <linux-sh@vger.kernel.org>
Link: http://lkml.kernel.org/r/20140223212736.774961401@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>