mesa/st: don't use serialized_nir for cached shaders
What does this MR do and why?
mesa/st: don't use serialized_nir for cached shaders
serialized_nir doesn't exist here, so just use the cached nir
fixes #11051
Fixes: 5eb0136a3c5 ("mesa/st: when creating draw shader variants, use the base nir and skip driver opts")