As I mentioned in issue #6332,

there return of a read operation that times out with no data received
is inconsistent:
```
Adafruit CircuitPython 7.3.0-beta.1-31-g73f6b4867-dirty on 2022-04-30; Adafruit Feather RP2040 with rp2040
>>>
>>> import board, busio
>>> print(board.UART().read(5))
None

Adafruit CircuitPython 6.3.0 on 2021-06-01; FeatherS2 with ESP32S2
>>> import board,busio
>>> print(board.UART().read(5))
None

Adafruit CircuitPython 7.3.0-beta.1 on 2022-04-07; Adafruit Feather STM32F405 Express with STM32F405RG
>>> import board, busio
>>> print(board.UART().read(5))
None

Adafruit CircuitPython 7.3.0-beta.1-31-g73f6b4867-dirty on 2022-04-28; Teensy 4.1 with IMXRT1062DVJ6A
>>> import board, busio
>>> print(board.UART().read(5))
b''
```

Since I have a PR on this file anyway, I thought I would put in the change to make it consistent
with the other 3 board types I tried.  Can not say about any of the others.

Author: KurtE

ports/mimxrt10xx/common-hal/busio/UART.c

@@ -428,6 +428,10 @@ size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t
         uint32_t recvd = 0;
         LPUART_TransferGetReceiveCount(self->uart, &self->handle, &recvd);
         LPUART_TransferAbortReceive(self->uart, &self->handle);
+        if (recvd == 0) {
+            *errcode = EAGAIN;
+            return MP_STREAM_ERROR;
+        }
         return recvd;
     }