Don't use padsv_nolv in attributed "my" declarations

When checking the optree constructed for "my" variables declarations with
attributes, disable the padsv_nolv optimisation that might have been done by
ck_padsv earlier.

I think that another, probably simpler and more efficient, approach to
implement the padsv_nolv optimisation would be to do it directly at optree
construction time, in my_kids() or my_attrs(), instead of doing that
optype-change dance in the ck functions.