af_unix: Return an error as a pointer in unix_find_other().

mainline inclusion
from mainline-v5.17-rc1
commit aed26f55
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4OM1C
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=aed26f557bbc94f0c778f63d7dfe86af99208f68



--------------------------------

We can return an error as a pointer and need not pass an additional
argument to unix_find_other().

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.co.jp>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Baisong Zhong <zhongbaisong@huawei.com>
Reviewed-by: Yue Haibing <yuehaibing@huawei.com>
Reviewed-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>