spirv: don't discard access set by vtn_pointer_dereference

We can have a access flag already set here so just augment the
existing ones.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 0fb61dfdeb ("spirv: propagate access qualifiers through ssa & pointer")
Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>

src/compiler/spirv/vtn_variables.c

@@ -2510,7 +2510,7 @@ vtn_handle_variables(struct vtn_builder *b, SpvOp opcode,
          struct vtn_pointer *ptr =
             vtn_pointer_dereference(b, base_val->pointer, chain);
          ptr->ptr_type = ptr_type;
-         ptr->access = access;
+         ptr->access |= access;
          vtn_push_value_pointer(b, w[2], ptr);
       }
       break;