USB: serial: add tiocmiwait subdriver operation

Add tiocmiwait operation to struct usb_serial_driver.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/usb/serial/usb-serial.c b/drivers/usb/serial/usb-serial.c
index 0b39d01..ada400d 100644
--- a/drivers/usb/serial/usb-serial.c
+++ b/drivers/usb/serial/usb-serial.c
@@ -402,10 +402,17 @@
 
 	dev_dbg(tty->dev, "%s - cmd 0x%.4x\n", __func__, cmd);
 
-	if (port->serial->type->ioctl)
-		retval = port->serial->type->ioctl(tty, cmd, arg);
-	else
-		retval = -ENOIOCTLCMD;
+	switch (cmd) {
+	case TIOCMIWAIT:
+		if (port->serial->type->tiocmiwait)
+			retval = port->serial->type->tiocmiwait(tty, arg);
+		break;
+	default:
+		if (port->serial->type->ioctl)
+			retval = port->serial->type->ioctl(tty, cmd, arg);
+		else
+			retval = -ENOIOCTLCMD;
+	}
 
 	return retval;
 }