udf: Remove redundant initialization of variable ret

After commit 9293fcfb

 ("udf: Remove struct ustr as non-needed
intermediate storage"), the variable ret is being initialized with
'-ENOMEM' that is meaningless. So remove it.

Link: https://lore.kernel.org/r/20200922081322.70535-1-jingxiangfeng@huawei.com
Signed-off-by: Jing Xiangfeng <jingxiangfeng@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>