btrfs: sysfs: normalize the error handling branch in btrfs_init_sysfs()

Although kset_unregister() can eventually remove all attribute files,
explicitly rolling back with the matching function makes the code logic
look clearer.

CC: stable@vger.kernel.org # 5.4+
Reviewed-by: NQu Wenruo <wqu@suse.com>
Signed-off-by: NZhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: NDavid Sterba <dsterba@suse.com>
Signed-off-by: NDavid Sterba <dsterba@suse.com>

fs/btrfs/sysfs.c

@@ -2321,8 +2321,11 @@ int __init btrfs_init_sysfs(void)
 
 #ifdef CONFIG_BTRFS_DEBUG
 	ret = sysfs_create_group(&btrfs_kset->kobj, &btrfs_debug_feature_attr_group);
-	if (ret)
-		goto out2;
+	if (ret) {
+		sysfs_unmerge_group(&btrfs_kset->kobj,
+				    &btrfs_static_feature_attr_group);
+		goto out_remove_group;
+	}
 #endif
 
 	return 0;