csky/kprobe: reclaim insn_slot on kprobe unregistration

On kprobe registration kernel allocate one insn_slot for new kprobe,
but it forget to reclaim the insn_slot on unregistration, leading to a
potential leakage.
Reported-by: NChen Guokai <chenguokai17@mails.ucas.ac.cn>
Reviewed-by: NMasami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: NLiao Chang <liaochang1@huawei.com>
Signed-off-by: NGuo Ren <guoren@kernel.org>

arch/csky/kernel/probes/kprobes.c

@@ -124,6 +124,10 @@ void __kprobes arch_disarm_kprobe(struct kprobe *p)
 
 void __kprobes arch_remove_kprobe(struct kprobe *p)
 {
+	if (p->ainsn.api.insn) {
+		free_insn_slot(p->ainsn.api.insn, 0);
+		p->ainsn.api.insn = NULL;
+	}
 }
 
 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)