intel: Drop the last uses of a mem_ctx in nir_builder_init_simple_shader().

These two consumers were the only ones out of the ~65 calls to
init_simple_shader, so there's a pretty clear consensus on how to allocate
simple shaders.  I suspect that actually these would be just fine with
b.shader being the mem_ctx, but that would take a bit more rework.

Acked-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7323>

src/intel/blorp/blorp_nir_builder.h

@@ -29,7 +29,8 @@ blorp_nir_init_shader(nir_builder *b,
                       gl_shader_stage stage,
                       const char *name)
 {
-   *b = nir_builder_init_simple_shader(mem_ctx, stage, NULL);
+   *b = nir_builder_init_simple_shader(NULL, stage, NULL);
+   ralloc_adopt(mem_ctx, b->shader);
    if (name != NULL)
       b->shader->info.name = ralloc_strdup(b->shader, name);
    if (stage == MESA_SHADER_FRAGMENT)