drm/xe/configfs: Rename configfs_find_group() helper

drm/xe/configfs: Rename configfs_find_group() helper

This helper name shouldn't suggest that it iss a part of the core
configfs API family. While around switch to use different helper
to release a reference.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250731193339.179829-7-michal.wajdeczko@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>