mimxrt10xx: Return proper UART read length when everything was read
mimxrt10xx: Return proper UART read length when everything was read

adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython,adafruit/micropython,adafruit/circuitpython,adafruit/micropython,adafruit/micropython,adafruit/circuitpython,adafruit/circuitpython