md: add missing sysfs_notify on array_state update

Changeset 6791875e has added early return from a function so there is no
sysfs notification for 'active' and 'clean' state change.

Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
Signed-off-by: Shaohua Li <shli@fb.com>