ac/nir/llvm: Fix setting function attributes for intrinsics

This fixes a NULL pointer dereference for intrinsics with more than
one function attribute introduced in commit 2fdaf38.
The fix is ported from the lp_build_intrinsic changes in commit 8bdd52c.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
1 file changed