Fix typo in header comment

Commit 4c04be9b0 accidentally left off the _id portion of the function
name in the header comment.

Author: Junwang Zhao <zhjwpku@gmail.com>
Discussion: https://postgr.es/m/CAEG8a3LP+ytnAXSzR=yiEaQrde+iCybMHsuPn9n=UN3puV_1tw@mail.gmail.com
