bcache: set pdev_set_uuid before scond loop iteration

There is no need to reassign pdev_set_uuid in the second loop iteration,
so move it to the place before second loop.

Signed-off-by: Yi Li <yili@winhong.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>