machine,nrf528,i2c: fix multiple resume-stop on bus error

[gen2thomas]

As already shown in #4998, in case of an error the i2c TX method in nrf528xx loops until a stop condition is fulfilled. In case of an error, a resume-stop command on bus will be called, so the bus can finish its work and exit the loop afterwards - no "hard" return in case of error is done and needed.

With the current code, after the first error occurs, each loop checks again for an error and practically (assuming the error is not gone) sends the resume-stop sequence again and again until the stop state is reached (triggered by the first resume-stop-sequence) and the loop is finished. On long run with existing errors, e.g the device is not connected on the bus, and cyclic calls (e.g. each 10 seconds) this leads reproducible to hang of the loop with the bme280 driver.

The provided code change improves the code for this topics:

• checks for the error code before the resume-stop is called, so the real error is finally contained in err variable
• skips the complete error check if the first error was detected - this fixes the originated problem

[eliasnaur]

LGTM, but please copy the relevant parts of the PR explanation to the commit message.

[gen2thomas]

@eliasnaur second topic added to the commit message - is the prefix ok? Is there a special guideline for commit messages on tinygo?

[eliasnaur]

I'm fairly new here, and not aware of particular guidelines for commit messages. My personal preference is to retain details in the commit message, because GitHub PRs are separate from the repository. That is, PR descriptions are for helping reviewers, and commit messages to describe the changes.

For your commit, I suggest something like

nrf528: stop the bus only once on I2C bus error

In some cases, e.g nothing connected on the bus, repeated resume-stop sequences can lead to the bus never reaching the stop state, hanging Tx.
This change ensures the resume-stop sequence is submitted once on error. It also moves the error code read to before the sequence to ensure it's valid.

Fixes: #4998