sysfs: include faulty drive in disk count

sysfs: include faulty drive in disk count

When the disk fails, it goes into faulty state first and it is removed
from the array in a while. It gives mdadm monitor a chance to see the disk
has failed and notify an event (e.g. FailSpare). It doesn't work when
sysfs is used to get a number of disks in the array as it skips faulty
disk. ioctl implementation doesn't differentiate between active and
faulty disk. Do the same for sysfs then. It should not matter that number
of disks reported is greater than list of disk structures returned by the
call because the same approach already takes place for offline disks.

Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>