Spinner readonly do not affect buttons

[ili]

I'm submitting a ... (check one with "x")

[x] bug report => Search github for a similar issue or PR before submitting
[ ] feature request => Please check if request is not on the roadmap already https://github.com/primefaces/primeng/wiki/Roadmap
[ ] support request => Please do not submit support request here, instead see http://forum.primefaces.org/viewforum.php?f=35

Plunkr Case (Bug Reports)
Please fork the plunkr below and create a case demonstrating your bug report. Issues without a plunkr have much less possibility to be reviewed.

http://plnkr.co/edit/XSfkhBgq14Sri3eCvCQP?p=preview

Current behavior
Readonly spinner can be edited with up & down buttons

Expected behavior
Up & down buttons should be disabled in readonly mode