livepatch/ppc32: Fix current backtracking in klp_check_calltrace

euler inclusion
category: bugfix
bugzilla: 51924
CVE: NA

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We through stack checking to ensure the consistency of livepatch.
Task blocked in __switch_to when switch out, thread_saved_fs/pc
store the FP and PC when switching, it can be useful when tracing
blocked threads. For running task, current_stack_pointer can be
used, but it's difficult to backtracking the running task on other
CPUs.

Fortunately, all CPUs will stay in this function, the current's
backtrace is so similar. so just backtracking the current on this
CPU, skip the current of other CPUs.

Signed-off-by: Cheng Jian <cj.chengjian@huawei.com>
Reviewed-by: Xie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: zhangyi (F) <yi.zhang@huawei.com>

Signed-off-by: Dong Kai <dongkai11@huawei.com>

Signed-off-by: Ye Weihua <yeweihua4@huawei.com>
Reviewed-by: Kuohai Xu <xukuohai@huawei.com>
Reviewed-by: Yang Jihong <yangjihong1@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>