Bugfix: Fix event handler for submit-via-enter in OcModal input

We fixed a small difference between clicking the confirm button and
hitting the enter key when using an OcModal with an input field, which 
lead to unexpected behaviour.

https://github.com/owncloud/owncloud-design-system/pull/2159
https://github.com/owncloud/web/pull/6961#pullrequestreview-979854434
