Change calling convention of 'edit_cylinder_info'

Change calling convention of 'edit_cylinder_info'

Instead of passing it the model and iterator (which requires that we
create the new entry for an 'add' event even if we then cancel the
operation), just make the caller do the final cylinder list update.

This way we can make 'add' work more sanely: if you cancel the add, we
now do not create an empty cylinder entry at the end.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>