Some terminology issues are fixed. (The speed of an UART interface is
the symbol rate. The unit it is measured in is baud, which is symbols
per second. There is no such thing as baudrate or even baud/s.)
The return codes are changed to use negative errno constants on error
to match the driver design rules. For backward compatibility, the
enum was updated to match the error codes. Unless an application
depends on the exact numerical value (which would be insane), this is
not breaking any code.
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