mips: Validate online cpus in irq_set_affinity() callbacks

The [user space] interface does not filter out offline cpus. It merily
guarantees that the mask contains at least one online cpu.

So the selector in the irq chip implementation needs to make sure to
pick only an online cpu because otherwise:

     Offline Core 1
     Set affinity to 0xe (is valid due to online mask 0xd)
     cpumask_first will pick core 1, which is offline

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Link: http://lkml.kernel.org/r/20140304203100.744800502@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/mips/sibyte/bcm1480/irq.c b/arch/mips/sibyte/bcm1480/irq.c
index 09d6e16..59cfe26 100644
--- a/arch/mips/sibyte/bcm1480/irq.c
+++ b/arch/mips/sibyte/bcm1480/irq.c
@@ -95,7 +95,7 @@
 	u64 cur_ints;
 	unsigned long flags;
 
-	i = cpumask_first(mask);
+	i = cpumask_first_and(mask, cpu_online_mask);
 
 	/* Convert logical CPU to physical CPU */
 	cpu = cpu_logical_map(i);