Non-existent event in asynchronous UART API

[Trubochkin]

There is an incorrect event name UART_RX_DONE :

zephyr/include/drivers/uart.h

Line 51 in c22f7e5

* - Ignore the event, this way when current buffer is filled UART_RX_DONE

Apparently the author made a mistake in the event name. There shuld be UART_RX_RDY