iris: Disallow incomplete resource creation

If a modifier specifies an aux, it must be created.

Fixes: 75a3947a ("iris/resource: Fall back to no aux if creation fails")
Reviewed-by: Sagar Ghuge <sagar.ghuge@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
(cherry picked from commit d298740a)