If you are using onchange="{! c.handleFilesChange }" on the lightning:input component, you can get the list of files by using the following command: event.getSource().get("v.files"), according to the docs.

I have tried it myself and it is working.

**..helper.js:**

    handleFilesChange : function(component, event)
    {
        var uploadFile = event.getSource().get("v.files")[0];
    }