system/fastboot: Fix Out-of-bounds Write

Signed-off-by: wangjianyu3 <wangjianyu3@xiaomi.com>

system/fastboot/fastboot.c

@@ -847,7 +847,7 @@ static void fastboot_command_loop(FAR struct fastboot_ctx_s *context)
 
   while (1)
     {
-      char buffer[FASTBOOT_MSG_LEN];
+      char buffer[FASTBOOT_MSG_LEN + 1];
       size_t ncmds = nitems(g_fast_cmd);
       size_t index;