Fix wrong temp readings with the default Maker Select V2 thermistor

[anibarro]

Number 13 it's way off for high temperatures (reading 220°C at around 240°C). Number 11 seems to match the readings of the stock Repetier firmware.

[andyrblank]

Hi, sorry for the delay on this request. I don't login to Github often. How did you verify this temperature? I don't have any way currently to confirm or deny the claim in this pull request and I haven't seen issues with the prints from this config. I'd be glad to accept the pull request if we can confirm it's validity. Thanks!

[anibarro]

Hi, I printed a temperature test model with the stock firmware before flashing the Marlin so I could compare both. Not the most accurate way, but I could also notice that out was taking much longer to reach 220°C.
At ambient temperature both settings read about the same value, but at 220 degrees I think there was an offset of around 20 degrees, just by looking at the test model that I printed before and after.
It would be great if someone could measure this in a more precise way