Input: add ps2_drain() to libps2 to allow reading and discarding
       given number of bytes from device. Change ps2_command to
       allow using 0 as command ID and actually pass it to the
       device instead of working as a drain.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
diff --git a/drivers/input/mouse/alps.c b/drivers/input/mouse/alps.c
index 2679a16..ffdc823 100644
--- a/drivers/input/mouse/alps.c
+++ b/drivers/input/mouse/alps.c
@@ -270,7 +270,6 @@
 static int alps_passthrough_mode(struct psmouse *psmouse, int enable)
 {
 	struct ps2dev *ps2dev = &psmouse->ps2dev;
-	unsigned char param[3];
 	int cmd = enable ? PSMOUSE_CMD_SETSCALE21 : PSMOUSE_CMD_SETSCALE11;
 
 	if (ps2_command(ps2dev, NULL, cmd) ||
@@ -280,7 +279,7 @@
 		return -1;
 
 	/* we may get 3 more bytes, just ignore them */
-	ps2_command(ps2dev, param, 0x0300);
+	ps2_drain(ps2dev, 3, 100);
 
 	return 0;
 }