drm/xe/configfs: Don't touch survivability_mode on fini

This is a user controlled configfs attribute, we should not
modify that outside the configfs attr.store() implementation.

Fixes: bc417e54 ("drm/xe: Enable configfs support for survivability mode")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Riana Tauro <riana.tauro@intel.com>
Reviewed-by: Stuart Summers <stuart.summers@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250904103521.7130-1-michal.wajdeczko@intel.com