arm-cci: fix handling cpumask_any_but return value

cpumask_any_but returns value >= nr_cpu_ids if there are no more CPUs.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576

Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

drivers/bus/arm-cci.c

@@ -1270,7 +1270,7 @@ static int cci_pmu_cpu_notifier(struct notifier_block *self,
 		if (!cpumask_test_and_clear_cpu(cpu, &cci_pmu->cpus))
 			break;
 		target = cpumask_any_but(cpu_online_mask, cpu);
-		if (target < 0) // UP, last CPU
+		if (target >= nr_cpu_ids) // UP, last CPU
 			break;
 		/*
 		 * TODO: migrate context once core races on event->ctx have