livepatch/x86: Ignore return code of save_stack_trace_tsk_reliable()

hulk inclusion
category: bugfix
bugzilla: 175666
CVE: NA
---------------------------

Checking return code of save_stack_trace_tsk_reliable() can be relaxed
for safety validation when appling livepatch, so we ignore it's return
code in klp_check_stack().

Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Reviewed-by: Jian Cheng <cj.chengjian@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>