ext2: Merge loops in ext2_xattr_set()

mainline inclusion
from mainline-5.3-rc1
commit 8cd0f2ba
category: bugfix
bugzilla: 174001
CVE: NA

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There are two very similar loops when searching xattr to set. Just merge
them.

Reviewed-by: Chengguang Xu <cgxu519@zoho.com.cn>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>