Fix misnamed variable breaking GNUstep

* src/nsterm.m (ns_set_offset): Use correct variable.

src/nsterm.m

@@ -1875,7 +1875,7 @@ Hide the window (X11 semantics)
 
          FIXME: Surely there's a better way than just hardcoding 100
          in here?  */
-      boundsRect.origin.x = 100;
+      topLeft.x = 100;
 #endif
     }