udf: destroy sbi mutex in put_super

Call mutex_destroy() on superblock mutex in udf_put_super()
otherwise mutex debugging code isn't able to detect that
mutex is used after being freed.
(thanks to Jan Kara for complete definition).

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/udf/super.c b/fs/udf/super.c
index 3ccb2f1..3d35a75 100644
--- a/fs/udf/super.c
+++ b/fs/udf/super.c
@@ -2300,6 +2300,7 @@
 		udf_close_lvid(sb);
 	brelse(sbi->s_lvid_bh);
 	udf_sb_free_partitions(sb);
+	mutex_destroy(&sbi->s_alloc_mutex);
 	kfree(sb->s_fs_info);
 	sb->s_fs_info = NULL;
 }