udf: Make udf exportable

Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Rasmus Rohde <rohde@duff.dk>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/super.c b/fs/udf/super.c
index b564fc1..260f4b82 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -1933,6 +1933,7 @@
 
 	/* Fill in the rest of the superblock */
 	sb->s_op = &udf_sb_ops;
+	sb->s_export_op = &udf_export_ops;
 	sb->dq_op = NULL;
 	sb->s_dirt = 0;
 	sb->s_magic = UDF_SUPER_MAGIC;