gallivm/nir: lower implicit lod to tex.

Fixes some sampling issues in vertex shaders

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4560>

src/gallium/auxiliary/gallivm/lp_bld_nir.c

@@ -1875,6 +1875,9 @@ void lp_build_opt_nir(struct nir_shader *nir)
       NIR_PASS_V(nir, nir_opt_constant_folding);
       NIR_PASS_V(nir, nir_opt_algebraic);
       NIR_PASS_V(nir, nir_lower_pack);
+
+      nir_lower_tex_options options = { .lower_tex_without_implicit_lod = true };
+      NIR_PASS_V(nir, nir_lower_tex, &options);
    } while (progress);
    nir_lower_bool_to_int32(nir);
 }