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: NFabian Frederick <fabf@skynet.be>
Signed-off-by: NJan Kara <jack@suse.cz>

fs/udf/super.c

@@ -2300,6 +2300,7 @@ static void udf_put_super(struct super_block *sb)
 		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;
 }