修复buzzer驱动的bug

buzzer.c

@@ -191,6 +191,11 @@ static ssize_t buzzer_write(struct file *filp, const char __user *buf,
     freq = (dev->buffer[2]<<8) + dev->buffer[1];
     duration = dev->buffer[3];
 
+    if(freq == 0)
+    {
+        return -EINVAL;
+    }
+
     if(status_flag == 1)
     {
         BeepOn(freq);