nir/spirv: Allow non-block variables with interface types in lists

The original objective was to disallow UBO and SSBO variables from the
variable lists.  This was accidentally broken in b208620fd when fixing some
other interface issues.

src/glsl/nir/spirv/spirv_to_nir.c

@@ -1816,7 +1816,7 @@ vtn_handle_variables(struct vtn_builder *b, SpvOp opcode,
       /* Interface block variables aren't actually going to be referenced
        * by the generated NIR, so we don't put them in the list
        */
-      if (var->interface_type)
+      if (var->interface_type && glsl_type_is_struct(var->interface_type))
          break;
 
       if (var->data.mode == nir_var_local) {