Ensure both input and output baud rates are set.

QSerialPortPrivate::setBaudRate() wasn't trying to set the output
baud rate for the port after successfully setting the input baud rate.

Also, some devices (such as FTDI chips) on Mac don't respond
properly if you call updateTermios() with mismatched baud rates,
even if you later set them to be the same.

Change-Id: I507fe10cba221bb4e43ded650dc44cc974de2414
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Reviewed-by: Laszlo Papp <lpapp@kde.org>