USB: qcserial: add Sierra Wireless EM74xx device ID

commit 04fdbc825ffc02fb098964b92de802fff44e73fd upstream.

The MC74xx and EM74xx modules use different IDs by default, according
to the Lenovo EM7455 driver for Windows.

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>