drm/xe/configfs: Use config_group_put()

drm/xe/configfs: Use config_group_put()

configfs has a config_group_put() helper that was adopted by
commit 88df7939d728 ("drm/xe/configfs: Rename struct xe_config_device").
Another pending work to add psmi later landed in commit
afe902848b41 ("drm/xe/configfs: Allow to enable PSMI") and didn't use
the helper.

Use config_group_put() consistently to hide the inner workings of
configfs. No change in behavior since it does exactly the same thing
as currently being done.

Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Link: https://lore.kernel.org/r/20250905162236.578117-2-lucas.demarchi@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>