LPC4322 serial port high baud rates bug

I noticed that for serial port configuration for high baud rates is do incorrect. For baud rates above 760000 baud error increases significantly and for example for 921600 real baudrate is 490384 (error almost 50%).

Start by reproducing the LPC4322 serial-port configuration at baud rates above 760000, comparing the requested rate with the reported real rate. Inspect the baud-rate setup and document the conditions that produce the large error. Done means high baud rates, including 921600, are configured with acceptable accuracy and the behavior is verified.

Written by the indexing model from the issue text.