kprobes: Cleanup collect_one_slot() and __disable_kprobe()

If kip->nused is not zero, collect_one_slot() return false, otherwise do
a lot of linked list operations, reverse the processing order to make the
code if nesting more concise. __disable_kprobe() is the same as well.

Link: https://lore.kernel.org/all/20240813115334.3922580-4-ruanjinjie@huawei.com/



Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>