USB: cp210x: initialise baud rate at open

commit cdc32fd6 upstream.

The newer cp2104 devices require the baud rate to be initialised after
power on. Make sure it is set when port is opened.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Cc: Preston Fick <preston.fick@silabs.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>