Manage: fix test for 'is array failed'.

We 'active_disks' does not count spares, so if array is rebuilding,
this will not necessarily find all devices, so may report an array
as failed when it isn't.

Counting up to nr_disks is better.

Signed-off-by: NeilBrown <neilb@suse.de>

Manage.c

@@ -827,7 +827,7 @@ int Manage_add(int fd, int tfd, struct mddev_dev *dv,
 			int d;
 			int found = 0;
 
-			for (d = 0; d < MAX_DISKS && found < array->active_disks; d++) {
+			for (d = 0; d < MAX_DISKS && found < array->nr_disks; d++) {
 				disc.number = d;
 				if (ioctl(fd, GET_DISK_INFO, &disc))
 					continue;