arm64: Avoid premature usercopy failure for __arch_copy_to_user_generic_read

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5MJU8


CVE: NA

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Commit 1b1b4ded ("arm64: Avoid premature usercopy failure") fixes an
usercopy failure issues, it introduced a variable srcin and used it in
fixup routine, but the variable is not initialized in
__arch_copy_to_user_generic_read(), this will cause an illegal pointer
issue in fixup.

Fixes: 1b1b4ded ("arm64: Avoid premature usercopy failure")
Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
Tested-by: yongqiang Liu <liuyongqiang13@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>