Exclude current node from entity reference view (for related news)
there is a patch fixing that issue and helping you to use [node:nid] as an arg here.



Otherwise, did you try Entity Reference View Widget ? 


  The module has a way of hiding selected items from the View. Simply
  add a base field contextual argument (Product ID for products, Node ID
  for nodes, etc) and in the "More" fieldset enable "Allow multiple
  values" and "Exclude". Then edit the Entity Reference field, and in
  the widget settings enable "Pass selected entity ids to View ".