tests/i915/module_load: restore gem_sanitycheck for discrete

This looks to be recently broken in: 5389b3f3
("tests/i915/i915_module_load: Use GEM_BUSY instead of SET_CACHE for
sanity check").

Which fails on discrete platforms, since we switched over to the
gem_busy ioctl, from the set_caching ioctl, which no longer gives
-ENODEV as the expected error.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/7420


Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Janga Rahul Kumar <janga.rahul.kumar@intel.com>
Cc: Priyanka Dandamudi <priyanka.dandamudi@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>