mdadm: Stop mdcheck_continue timer when mdcheck_start service can finish check

mdadm: Stop mdcheck_continue timer when mdcheck_start service can finish check

mdcheck_continue is triggered by mdcheck_start timer. It's used to
continue check action if the raid is too big and mdcheck_start
service can't finish check action. If mdcheck start can finish check
action, it doesn't need to mdcheck continue service anymore. So stop
it when mdcheck start service can finish check action.

Signed-off-by: Xiao Ni <xni@redhat.com>
Acked-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Signed-off-by: Jes Sorensen <jes@trained-monkey.org>