staging: serqt_usb2: remove unneeded return in qt_unthrottle

this return is at the end of the void function qt_unthrottle, which is
not needed, and also remove the new line below this.
Signed-off-by: Devendra Naga <develkernel412222@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/serqt_usb2/serqt_usb2.c

@@ -1499,8 +1499,6 @@ static void qt_unthrottle(struct tty_struct *tty)
 		}
 	}
 	mutex_unlock(&qt_port->lock);
-	return;
-
 }
 
 static int qt_calc_num_ports(struct usb_serial *serial)