fail_function: refactor code of checking return value of register_kprobe()

Refactor the error handling of register_kprobe() to improve readability. 
No functional change.

Link: https://lkml.kernel.org/r/20220826073337.2085798-2-yangyingliang@huawei.com


Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>