[BUGFIX] Use correct variable name in OnlineMedia.js

Resolves: #86630
Releases: master, 8.7
Change-Id: I4bce2665ed54cddc3a151445c5863c24ffac6df6
Reviewed-on: https://review.typo3.org/58622
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>

typo3/sysext/backend/Resources/Public/JavaScript/OnlineMedia.js

@@ -36,7 +36,7 @@ define(['jquery',
     me.irreObjectUid = me.$btn.data('file-irre-object');
     me.allowed = me.$btn.data('online-media-allowed');
     me.allowedHelpText = me.$btn.data('online-media-allowed-help-text') || 'Allow to embed from sources:';
-    me.btnSubmit = me.$btn.data('data-btn-submit') || 'Add';
+    me.btnSubmit = me.$btn.data('btn-submit') || 'Add';
     me.placeholder = me.$btn.data('placeholder') || 'Paste media url here...';
 
     /**