drm/xe/configfs: Free ctx_restore_mid_bb in release

ctx_restore_mid_bb memory is allocated in wa_bb_store(), but
xe_config_device_release() only frees ctx_restore_post_bb.

Free ctx_restore_mid_bb[0].cs as well to avoid leaking the allocation
when the configfs device is removed.

Fixes: b30d5de ("drm/xe/configfs: Add mid context restore bb")
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Nitin Gote <nitin.r.gote@intel.com>
Link: https://patch.msgid.link/20260225013448.3547687-2-shuicheng.lin@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
(cherry picked from commit a235e7d)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

Author: ShuichengLin

drivers/gpu/drm/xe/xe_configfs.c

@@ -830,6 +830,7 @@ static void xe_config_device_release(struct config_item *item)
 
 	mutex_destroy(&dev->lock);
 
+	kfree(dev->config.ctx_restore_mid_bb[0].cs);
 	kfree(dev->config.ctx_restore_post_bb[0].cs);
 	kfree(dev);
 }