drm/i915/guc: re-optimise i915_guc_client layout

As we're tweaking the GuC-related code in debugfs, we can
drop the no-longer-used 'q_fail' and repack the structure.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>