USB: serial: Add Option GTM681W to qcserial device table.

The Option GTM681W uses a qualcomm chip and can be
served by the qcserial device driver.

Signed-off-by: Richard Weinberger <richard@nod.at>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>