drm/xe/configfs: Destroy xe_configfs.su_mutex on exit/error

drm/xe/configfs: Destroy xe_configfs.su_mutex on exit/error

While mutex_destroy() is NOP when CONFIG_DEBUG_MUTEXES is not
enabled, we should still call it.

While around, drop a trailing line.

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/20250731193339.179829-4-michal.wajdeczko@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>