mm: reliable: Return corrent errno in reliable_check

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4SK3S


CVE: NA

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LTP's proc01 test was failing be because this ret code (1):

	proc01      1  TFAIL  :  proc01.c:400: read failed: /proc/self/task/1406366/reliable: errno=EPERM(1): Operation not permitted

To slove this problem, return corrent errno in reliable_check().

Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>