With CLONE_IO, copy_io() increments both ioc->refcount and ioc->nr_tasks.
However exit_io_context() only decrements ioc->refcount if ioc->nr_tasks
reaches 0.

Always call put_io_context() in exit_io_context().
Signed-off-by: NLouis Rilling <louis.rilling@kerlabs.com>
Signed-off-by: NJens Axboe <jens.axboe@oracle.com>