Fix gas resistance reading

[felmue]

There is a report in the M5Stack community forum about ENVPro unit not properly reporting gas resistance.

I looked through the code and I think there might be a copy / paste error here.

Note: I do not have an ENVPro unit therefore I cannot test this myself - so I could be wrong here.

Thanks
Felix

[lbuque]

@felmue The lib for the bem688 is based on https://github.com/adafruit/Adafruit_CircuitPython_BME680, which I recently discovered had some updates done again and I can't tell if it works as expected.

I'm thinking of writing a library for the bme688 using the C binding approach.