QtcPlugin.qbs: use the right name binding in Group

We're going to add the property Group.name in qbs.
Consequently, Groups must use product.name when accessing the name of
the product.

Change-Id: Id2527300a8a7c26bb742d4111f9d47ded6c492b1
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>

src/plugins/QtcPlugin.qbs

@@ -29,7 +29,7 @@ Product {
     }
 
     Group {
-        files: [ name + ".pluginspec.in" ]
+        files: [ product.name + ".pluginspec.in" ]
         fileTags: ["pluginSpecIn"]
     }
 }