修复buzzer驱动bug

buzzer.c

@@ -188,7 +188,7 @@ static ssize_t buzzer_write(struct file *filp, const char __user *buf,
     dev->size = count;
 
     status_flag = dev->buffer[0];
-    freq = dev->buffer[2]<<8 + dev->buffer[1];
+    freq = (dev->buffer[2]<<8) + dev->buffer[1];
     duration = dev->buffer[3];
 
     if(status_flag == 1)