etmem: etmem scan module Replace WARN_ONCE() with debug_printk for "nothing read"

euleros inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I7RO5Q
CVE: NA
Reference: https://gitee.com/openeuler/kernel/commit/79246e864484015e1ef3c7ecec2d18a6b27199ec



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The etmem_scan.ko module is used to scan the process memory.

The specific usage is as follows:
The etmem user mode process issues scan commands through
/proc/pid/idle_pages, and the etmem_scan module scans
based on the issued address information.

Under certain circumstances, the phenomenon that the scan result
is empty may occur. This phenomenon is a normal logic flow and
does not need to print the log through WARN_ONCE.

Therefore, Replace WARN_ONCE() with debug_printk for "nothing read"

Signed-off-by: liubo <liubo254@huawei.com>
Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>