Fix function name typo

[autoelk]

The description above describes a function called update but the code below uses write_once

[clarksmr]

Thanks for noticing the discrepancy! Code later in the file (not touched by 46c4740), though, also uses write_once. So either we have to switch everything to update, or everything to write_once. For sake of a more precise function name, I'm going to go with the latter.