Properly limit keyboard keycodes to KEY_MAX.

It can only be set by root, but let's not tempt people to do
things that can't work.

drivers/char/keyboard.c

@@ -198,6 +198,8 @@ int setkeycode(unsigned int scancode, unsigned int keycode)
 
 	if (scancode < 0 || scancode >= dev->keycodemax)
 		return -EINVAL;
+	if (keycode < 0 || keycode > KEY_MAX)
+		return -EINVAL;
 
 	oldkey = SET_INPUT_KEYCODE(dev, scancode, keycode);