nir: s/nir_var_mem_image/nir_var_image/g

We typically use nir_var_mem_* for stuff that has an explicit byte-based
memory layout.  Images are opaque.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/13386>

src/compiler/nir/nir_divergence_analysis.c

@@ -603,7 +603,7 @@ nir_variable_mode_is_uniform(nir_variable_mode mode) {
    case nir_var_mem_ssbo:
    case nir_var_mem_shared:
    case nir_var_mem_global:
-   case nir_var_mem_image:
+   case nir_var_image:
       return true;
    default:
       return false;