livepatch/arm64: Uniform 'old_func' field in struct klp_func_node

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4UAQ1



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'struct klp_func_node' is used to save codes of a function which is then
be live-patched. Currently this structure is respectively defined in
x86/arm32/arm64/ppc32/ppc64.

The definitions of field which save old function address are different:
  In x86/arm32/ppc32/ppc64: void *old_func;
  In arm64: unsigned long old_addr;

Minority subordinates to majority, uniform them as 'void *old_func'.

Preparatory only, no functional change.

Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>