Citing Ramanujan's notebooks
There is some inconsistency in how different sources list Ramanujan's Notebooks and the two people deserving credit for it:


The Library of Congress catalog entry lists Ramanujan a bit ambiguously under "Personal name", but describes the work as "edited by" Berndt.
The British Library catalog entry lists Ramanujan under "Author" and Bruce Berndt under "Contributor" with the notation "Ed." (again implying that Berndt's role is that of editor).
Google Books lists Bruce Berndt as "Editor" and has the convoluted string "Srinivasa Ramanujan Aiyangar Bruce C. Berndt, Bruce C. Berndt, Ramanujan" under "Author".


It sounds like these three sources pretty much agree that Ramanujan is an author and Berndt is an editor. I don't know if there's an authoritative answer to the question of whether Bruce Berndt is also a co-author. I can only assume that either one of the famous national libraries I linked to above would be regarded as authoritative enough that no one will fault you for relying on their listings.

From a more philosophical point of view, whether Bruce Berndt is considered an editor or author is immaterial. His compilation and editing of Ramanujan's original notebooks was a monumental achievement, and that is what really matters.