ea3c73b33c
nir_builder_at requires a block to chase back to the function impl,
but for an empty function impl, the previous code produced a cursor
with a null pointer. It was also just extra complicated.
While I'm here, use the new foreach helper since this code needs an impl.
Fixes: 12a268ea ("microsoft: Use nir_builder_at")
Reviewed-by: Eric Engestrom <eric@igalia.com>
Acked-by: Daniel Stone <daniels@collabora.com>
Acked-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24042>