[smart] fix of cmd_kill (#8071)

Signed-off-by: Shell <smokewood@qq.com>

components/lwp/lwp_pid.c

@@ -857,7 +857,7 @@ MSH_CMD_EXPORT(list_process, list process);
 static void cmd_kill(int argc, char** argv)
 {
     int pid;
-    int sig = 0;
+    int sig = SIGKILL;
 
     if (argc < 2)
     {

components/lwp/lwp_signal.c

@@ -690,7 +690,7 @@ rt_err_t lwp_signal_kill(struct rt_lwp *lwp, long signo, long code, long value)
     /** must be able to be suspended */
     RT_DEBUG_SCHEDULER_AVAILABLE(RT_TRUE);
 
-    if (!lwp || signo < 0 || signo >= _LWP_NSIG)
+    if (!lwp || signo <= 0 || signo > _LWP_NSIG)
     {
         ret = -RT_EINVAL;
     }