mod_push: Fix API call return type on error

A call that yields a 'rescode' isn't supposed to return an error tuple.

src/mod_push.erl

@@ -243,9 +243,9 @@ delete_old_sessions(Days) ->
 	[] ->
 	    ?INFO_MSG("Deleted push sessions older than ~B days", [Days]),
 	    ok;
-	[NotOk | _] ->
+	[{error, Reason} | _] ->
 	    ?ERROR_MSG("Error while deleting old push sessions: ~p", [NotOk]),
-	    NotOk
+	    Reason
     end.
 
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