USB: cp210x: initialise baud rate at open

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>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>