ublk: return -EINTR if breaking from waiting for existed users in DEL_DEV

If user interrupts wait_event_interruptible() in ublk_ctrl_del_dev(),
return -EINTR and let user know what happens.

Fixes: 0abe39de ("block: ublk: improve handling device deletion")
Reported-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Link: https://lore.kernel.org/r/20230726144502.566785-4-ming.lei@redhat.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>