USB: cdc-acm: remove redundant usb_mark_last_busy

There's no need to call usb_mark_last_busy after having increased the PM
counter in write(). The device will be marked busy by USB core when the
PM counter is balanced in the completion handler.
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-acm.c

@@ -690,7 +690,6 @@ static int acm_tty_write(struct tty_struct *tty,
 		spin_unlock_irqrestore(&acm->write_lock, flags);
 		return count;
 	}
-	usb_mark_last_busy(acm->dev);
 
 	stat = acm_start_wb(acm, wb);
 	spin_unlock_irqrestore(&acm->write_lock, flags);