Fix weird uses of num_online_cpus().

This may be OK in archs with contiguous CPU numbers and without
hotplug CPUs, but it sets a terrible example.

And open-coding it like drivers/scsi/hpsa.c is just weird.

BTRFS has a weird comparison with num_online_cpus() too, but since
BTRFS just screwed up my test machines' root partition, I'm not
touching it :)

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Reported-by: Oleg Drokin <green@linuxhacker.ru>
diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
index a1cfbd3..8eab107 100644
--- a/drivers/scsi/hpsa.c
+++ b/drivers/scsi/hpsa.c
@@ -6632,14 +6632,12 @@
 
 static void set_lockup_detected_for_all_cpus(struct ctlr_info *h, u32 value)
 {
-	int i, cpu;
+	int cpu;
 
-	cpu = cpumask_first(cpu_online_mask);
-	for (i = 0; i < num_online_cpus(); i++) {
+	for_each_online_cpu(cpu) {
 		u32 *lockup_detected;
 		lockup_detected = per_cpu_ptr(h->lockup_detected, cpu);
 		*lockup_detected = value;
-		cpu = cpumask_next(cpu, cpu_online_mask);
 	}
 	wmb(); /* be sure the per-cpu variables are out to memory */
 }