[encryption] always use oc view

always a OC Filesview to access the files.

As discussed here: https://github.com/owncloud/core/issues/8936
Okay, I suppose that's the one I mentionned above.
You didn't specify `0750, true` above, possibly because `$view->mkdir()` doesn't support this.
I assume you checked that `$view->mkdir()` is automatically creating the parents.