draw: free the NIR IR.

Not sure how I missed this, the ownership was a bit blurry,
free the NIR.

Fixes: bf12bc2dd7a2 (draw: add nir info gathering and building support)
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4563>
2 files changed