nir/spirv: don't use bare types, remove assert in split vars for testing

nir/spirv: don't use bare types, remove assert in split vars for testing

For OpenCL we never want to strip the info from the types, and it makes
type comparisons easier in later stages. We might later need a nir pass to
strip this for GLSL, but so far the only regression is the assert and Jason
said removing that is fine.

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>