键盘状态扫描函数
/*
键盘扫描函数
读取当前键盘的状态
有按键按下返回相应按键值
无按键按下返回"0x00"
*/
-Keyboard status scan function/* keyboard scan function to read the current state of the keyboard keys have a corresponding button press to return to the value of non-button press to return to
This driver is based on the 2.6.3 version of drivers/usb/usb-skeleton.c
but has been rewritten to be easy to read and use, as no locks are now
needed anymore.