btrfs: sysfs: unexport space_info_ktype

The last non-sysfs usage of space_info_ktype has been moved to a private
helper in previous patch so the variable can be made static.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/sysfs.c

@@ -395,7 +395,7 @@ static void space_info_release(struct kobject *kobj)
 	kfree(sinfo);
 }
 
-struct kobj_type space_info_ktype = {
+static struct kobj_type space_info_ktype = {
 	.sysfs_ops = &kobj_sysfs_ops,
 	.release = space_info_release,
 	.default_groups = space_info_groups,

fs/btrfs/sysfs.h

@@ -79,7 +79,6 @@ attr_to_btrfs_feature_attr(struct attribute *attr)
 
 char *btrfs_printable_features(enum btrfs_feature_set set, u64 flags);
 extern const char * const btrfs_feature_set_names[FEAT_MAX];
-extern struct kobj_type space_info_ktype;
 int btrfs_sysfs_add_device_link(struct btrfs_fs_devices *fs_devices,
 		struct btrfs_device *one_device);
 int btrfs_sysfs_rm_device_link(struct btrfs_fs_devices *fs_devices,