afbr-s50: Add graceful error-handling on data-ready

Whenever the data-ready callback is invoked, there's a common pattern
that needs to take place:

- Stop measurement timer (to stop on-coming samples), which could be
restored by the application re-submitting the request.
- Set iodev_sqe to NULL, so new requests can come in.
- Report the error on the SQE.

This has been refactored in handle_error_on_result() and now it's
invoked throughout the code.

Signed-off-by: Luis Ubieda <luisf@croxel.com>